My first long distance swim was from Robben Island to Cape Town when I was 17 years old. It was a 7km swim and the water was around 17°C. I barely made it. I was very thin. (Body fat definitely helps insulate you from the cold) The first 2 hours were fine, but after that I got very cold, so the last hour was a major struggle. I ended up swimming breaststroke. Finally, after 3 hours, I put my feet down and felt sand. It was the most amazing feeling ever!

I always love the feeling of diving into the ocean. No matter how tough my day has been, when I am in the sea, the world seems perfect.

It would be a toss up between my swim across the North Pole in 2007 and my swim across a glacial lake on Mt Everest in 2010. Both were immensely challenging. At the North Pole the water was minus 1.7°C (29°F). It’s the coldest seawater goes before it freezes. On Mt Everest, the water was 2°C (35°F) and I was also swimming at 5,500m where there’s little oxygen. So I had to swim slowly just to breathe; but the slower I swam, the colder I got. It was a dangerous cocktail.

Yes. I have pulled out of a few swims for safety reasons. I value my life.

A very short period of time - a few minutes maximum. When you dive into freezing cold water, it’s very difficult to breathe. You gasp for air. The water will be around minus 1.7°C. That’s 7°C colder than the water in which the passengers of the RMS Titanic perished. If you have not trained in those conditions, you’ll swallow water and drown.

We prepare thoroughly, to mitigate against them as best as possible. But in my world I have to face cold water, predators (including polar bears, sharks, walruses and leopard seals), strong currents, shipping hazards and political instability. That having been said, there’s a fine line between bravery and stupidity, which should never be crossed.

Being the first person to swim around a cape or across a lake or down a river is always special. But I swim because I want to draw attention to the state of our oceans – and get them protected. And if you are first, it gets a lot more media attention. So being first is important.

I ask world leaders to do everything they can to protect our environment. However, sometimes the legislation I ask them to enact is unpopular with the electorate. If I am asking them to be courageous, I must also be. Swimming in a wetsuit or a drysuit would not send the right message. So I swim according to Channel Swimming Rules - i.e. in just a Speedo swimming costume.

No. Many Channel swimmers use grease to keep warm. I’ve swum in the English Channel with grease and without grease, and it does not seem to make much difference. So I no longer use it.

It depends on the swim. If it’s a multi-day swim, I train for many hours each day. The polar swims require less time in in the sea. For them I do weights and sprints.

You can never spend too much time on technique. I always tell young swimmers: 'Practice things until you can't get them wrong. Not until you get them right.' There's a big difference.

I love the oceans and have seen them change in my lifetime. So I undertake swims in the most vulnerable parts of our oceans to campaign for the creation of Marine Protected Areas, which are akin to National Parks in the sea.

I’ve seen enormous chunks of ice slide off Arctic glaciers. I’ve swum over bleached coral killed by rising sea temperatures, and over the bones of whales hunted to the edge of extinction. I’ve visited lakes high in the Himalayas where once there was only ice. And I've seen plastic pollution in the most remote areas where no humans have set foot. I’ve seen drastic changes in my lifetime – changes that have come about because of our actions.

I don’t think I am either. I describe myself as an ocean advocate and a pioneer swimmer.

Yes, I worked as a maritime lawyer for five years in two London law firms.

It was a good grounding, but it wasn’t for me. Like anything in life, you need to be passionate about it to succeed. And ever since I was a young boy I dreamt of exploring the oceans. Full time law put me behind the desk too much.

It taught me how to argue passionately and rationally. That’s key to being a successful environmental campaigner. If you are too emotional you run the risk of turning off policy makers. And if you can’t present your arguments rationally, no one will listen to you.

Many things. Most importantly I learned how to work in a team in very challenging circumstances.

I have a meeting with the 75-year-old me. That person usually knows what to do.

Oceans inspire me. There’s nothing I enjoy more than diving into the Atlantic Ocean and going for a long swim. In terms of people my heroes as a young boy were David Livingstone, Roald Amundsen and Sir Edmund Hillary - men who pushed boundaries and who were pioneers. I wanted to be an aquatic version of them. Swimming in places where no one had swum before. And swimming for a reason. And then of course my parents, who took me to many National Parks as a child and inspired my love for nature.

My mother would top the list. She is very, very loving. She read a lot to me as a child.

I think it’s important to find your purpose in life, and then pursue it with passion. It took me time to recognize my purpose – but I am now definitely on the right road.

First, always speak from the heart. Second, drop PowerPoint. Tell a story. Everyone loves a story. And finally, make sure you have stopped talking before your audience has finished listening.

It varies, but around 100.

I love it.

If you have a passion, follow it. It's the best barometer of what you will be good at. And choose a career that you enjoy – the extra money of a job you detest isn’t worth it.

I am very focused. I have to dive in with 100% commitment. If I dived in with thoughts of victory and defeat at the same time, I’d be out the water in seconds.

No I tolerate it. Anyone who says they love swimming in freezing water is either lying or has never done it. I swim in these places to carry a message about what we are doing to our environment. There’s nothing more symbolic than swimming across a place, which used to be frozen over and now is open sea.

It’s subconscious. It just happens. My core body temperature rises from 37°C to 38.2°C before I get into freezing water. That does not sound like a lot, but if your core body temperature rises more than 2°C you are clinically hyperthermic. Drop 2°C and you are clinically hypothermic. So being able to raise my core body temperature by 1.2°C makes an enormous difference. It enables me to stay in freezing water for prolonged periods of time. Professor Tim Noakes, who recorded this phenomenon, coined the phrase 'anticipatory thermo-genesis' (creation of heat before an event). We don’t know what causes it. I think it’s simply a Pavlovian Response. I have been swimming in cold water for nearly 30 years. My body knows what is needed. So subconsciously it heats up to protect me.

Unfortunately yes. I say unfortunately as I hoped it would become like the mountaineer’s '7 Summits', where they climb the highest mountain on every continent. But only a handful of swimmers have undertaken a long distance swim in the Arctic Ocean or Southern Oceans.

I think it foolhardy to predict the absolute limits of human endurance.

It depends. If I'm doing a long swim in a warm ocean, I just enjoy the moment and dream. If I'm swimming in a polar region I concentrate on each stroke – trying to make it the best possible action. I don’t want to be in the freezing water any longer than necessary.

Yes, I have a large support team. For example, when I swam across the North Pole, my team consisted of 29 people. They came from 10 nations. It included a doctor, 2 scientists, 2 cameramen, my coach, 2 boat drivers and 3 polar bear guards.

Someone who can balance confidence and humility. You need both. I also like people who are optimistic realists. Not daydreamers, and certainly not pessimists.

Yes, too little confidence, and you're unable to act; too much confidence, and you're unable to hear.

I love swimming around Robben Island in South Africa. The view of Table Mountain is spectacular. And it’s made all the more special when I see penguins swimming underneath me.

First, secure the most experienced pilot, who’ll find you the shortest route across. Second, have patience. Swimmers get frustrated and pick the wrong day to cross. Timing is everything. Third, do your cold-water training. Water that is 18°C (64°F) feels icy after 15 or 20 hours. Fourth, have someone inspiring on your boat that can make good judgment calls and keep you going when you are exhausted. And last, when you swim from England to France you’ve got to leave your doubts on the beach at Dover.

Very few things are impossible to achieve – if you put your mind to it. That’s the key – really putting your mind to it. When you’ve got purpose everything becomes possible. And obviously – don’t quit. Many battles are only won in the 11th hour.

I look for swims where I can carry a powerful message. No message, no swim. I don’t get wet now unless it’s for a reason.

It was more a slow awakening. I visited many National Parks as a young boy. And I loved spending time in wilderness areas. Then as a swimmer I began to notice how the oceans were changing. Every year I would see less and less fish. And more pollution. Then in 2005 I undertook a swim at Deception Island off Antarctica. There had been a whaling station there many years before. Under the water there were hundreds of whale bones discarded there by the hunters. Some of them were piled so high that, when I took a stroke, my hands touched them. It revolted me. After the swim I could not get the images out of my mind. I realized I had to stand up and be a voice for the oceans.

Yes, of course. It was impossible not to be inspired by people like Nelson Mandela, Desmond Tutu and Molly Blackburn. Men and women who stood up for freedom, equality and justice. Each generation will be faced with its challenges. But the ones we face today are like none we have ever faced before. The destruction of our environment threatens our very existence. To simply watch is unfold is not an option.

Agreed. But the most important human rights issue facing the world today is the world.

I’ve swum through some very cold and rough seas. I think that’s made me more determined than the average person.

A few times. But when it starts happening I say to myself 'Lewis can you take another 100 strokes?' And normally I can. And when they are up I try and take another 100. And eventually I get to the other shore. That’s the only way you can think when you’re swimming in a polar region.

Yes, three swims.

It’s part of being a pioneer swimmer. You've got to be willing to fail and try again. The point isn’t to learn to fail, the point is to learn to bounce back.

If things are not done properly on our expeditions one of us could lose our lives. That’s why we always insist on doing everything, even the smallest things, with an 'unrelenting pursuit of excellence'. It’s also the easiest and quickest way to get a job done. It saves everyone time because you don’t have to do the job over. Finally, excellence is great for morale. Imagine working for a team where mediocrity is standard. It must be so demotivating.

No. I find perfection demotivating. I mean, how often do we achieve perfection? There's a tyranny in perfection. Just do things to the very best of your ability. Then move on.

I’m honoured. What I most admired about Sir Ed was that after summiting Mt Everest he returned to build many schools, bridges and hospitals. He served the people of Nepal tirelessly. “Giving back” is the missing link in modern sport.

Two things: ignorance and purpose. Ignorance of just how tough the path ahead will be. If you knew how tough it would be, you’d probably not take it. And a driving purpose, which keeps you going nonetheless.

It’s very important. My mind has to be ready. My body also has to be ready. But even more important, my heart has to be ready. What I mean by that is for the swims I do, I must have a burning reason.

You have to train for the conditions you will be swimming in. So when I am preparing for a polar swim I train in the coldest water I can find. It’s not fun. But it is necessary. It also helps prepare my mind.

Yes. Being the first to undertake a swim is exponentially harder than going second. You don’t know what will happen. The fear can be crippling. It’s much easier to go second. You know it’s possible. The world is divided into pioneers and followers. You are one or the other. I prefer to be a pioneer.

The trick is to make fear your friend. Fear forces you to prepare more rigorously and see potential problems more quickly.

Yes. To do anything worthwhile, you will face periods of grinding doubt and fear. You need to mitigate against the risks. Then somehow put the fear to one side. And keep moving forward.

That’s not possible. The mind will always let you down first. Once the mind accepts the impossible is achievable, the body soon follows. And vice versa.

It’s crucial. But the most powerful form of self-belief does not come from within. It comes from the outside. It comes from believing in something greater than you.

I’ve been swimming for 28 years, and I don’t think there is one swim where someone didn’t say beforehand, 'I don’t think it’s possible', or 'You’ll never make it'. If someone tells you that you can’t achieve your dream, don’t waste good time arguing. Just walk away and do it.

Yes, they are expensive. But securing sponsors has become easier. The key is to make sure every expedition is bigger, harder and hopefully more inspiring than the one before.

Don’t go into a meeting with a spreadsheet, a business plan or a PowerPoint presentation. Sponsors invest in dreams. Share your dream.

Absolutely. I constantly dream. One of the ironies I’ve found with dreaming is that it’s much easier to achieve a big dream than it is a small one. Big dreams require big passion. And when you’ve got passion it’s easier to inspire others to come along and help you.

I help spearhead the UN’s campaign for more Marine Protected Areas around the world. MPAs are basically National Parks in the Oceans. Less than 2% of the world’s oceans are protected. We must change that.

There are many. When we set aside MPAs we protect the marine habitat. When we do that, fish stocks recover. Which supports food security. When we create MPAs, we protect the coral, which protects the shoreline and provides shelter for fish. Marine Protected Areas are places people want to visit for ecotourism, so it's good for the economy. It has, if you'll pardon the pun, a ripple effect. Marine Protected Areas are good for the world economy, for the health of the oceans, for every person living on this planet.

Aside from the Polar Regions, there are three places I love returning to - and they all begin with the letter N. First is Norway as the fjords are simply magnificent. Second is Namibia for the sand dunes and isolation; I love the Skeleton Coast. And third is Nepal for the warmth, humility and generosity of its people.

Who doesn’t love a penguin? They’re cool They all have distinct personalities, just like humans. Some are dozy, some are happy, some are grumpy, some of them are thieves – stealing other penguin's nesting rocks. And all of them have sharp beaks.

The Mediterranean, Adriatic, Aegean, Black, Red, Arabian and North Seas. Essentially the seas that surrounded the ancient world.

The North Sea - there was a strong headwind for most of the swim, which made swimming conditions very challenging.

I knew that the Seven Seas are amongst the most overfished in the world, but I was shocked by the extent of the damage. In four weeks of swimming I did not see one fish longer than 30cm, in any of the seas. And I saw not one shark. No dolphins. And no whales.

Yes, a healthy ocean is an ocean with sharks. Take away an apex predator and it’s like removing the lions from the Serengeti. It won’t be long before the gazelle, zebras and wildebeest have multiplied and eaten all the grass. And when the land is laid bare the grazers will starve to death. Predators are crucial for a healthy ecosystem – be it on land or in the water.

Yes. An estimated 100 million sharks are fished out of the world's oceans every year. Take a minute to mull over that figure. That's over a quarter of a million animals each day. If this number of humans were killed in a year, it would be called genocide. There is a name for what is happening in our oceans today: it is ecocide.

I saw the most sea life in the Arabian Sea. I saw vast shoals of Green Turtles (a protected species in Oman), which was spectacular.

It’s confirmed my view that we urgently need to set aside big chunks of our oceans as Marine Protected Areas. I see protecting our environment as a human rights issue. The right to have our environment protected for the benefit of our generation and future generations is our most important human right.

I will never forget the people we met along the way, the literally hundreds of people from all walks of life who helped us and supported us and jumped in the sea to swim with us, just to be part of our mission, just for their love of the sea.

I urge everyone to raise their voices. The more we talk about MPAs, the more we educate ourselves and others about the issues and the urgency, the more governments know that we want them, the more they will happen.

It was during my swim in the Red Sea. I swam through a Marine Protected Area, and experienced the sea as it was meant to be: rich and colourful, teaming with abundant life. It was simply breath- taking. But then, just two kilometres on, outside of the protected area, there was no coral and there were no fish. It looked like an underwater desert. If I had needed more proof that Marine Protected Areas really work, that was it.

Fortunately nothing was life threatening. Exhausting though – the final swim in the North Sea was 60km. So at the end I was finished.

So many people helped me during the expedition. In total there were over 200 people. No matter how tired I was, I simply could not let them down.

It’s a long-term project to persuade governments to set aside large parts of our oceans as Marine Protected Areas. I met a number of key policy makers en route and will be having follow up meetings with them in the weeks to come. But it was very pleasing to see that our message was shared on social media by a wide range of organizations from the World Economic Forum to the United Nations and Greenpeace.

Don’t be afraid of going against the tide.

Between London and Cape Town.

Walking on the beach with my three dogs.

Chocolate ...

Cruelty to animals. I simply can’t understand why anyone would want to hurt an animal.

Yes, monotony.

Have you seen the colour of my hair?

I still have many more swims and campaigns planned.

'Sometimes it falls upon a generation to be great, you can be that generation,' by Nelson Mandela.