I WASN'T sure what to expect. It had been, by my reckoning, about a year since I first approached his PR people and asked to interview him.

For whatever reason he had been less than enthusiastic. In fact the message which got relayed to me was Pen 'didn't see how it would benefit him'.

I just mumbled my thanks to them for trying to persuade him and I put the phone down, frustrated and disappointed.

At the time I hadn't realised Pen was furiously fundraising and in his fourth year of preparing for the Catlin Arctic Survey.

So I guess unless I was able to contribute towards the £5million cost of the expedition, he literally didn't have the time for an interview.

Almost 12 months and several phone calls later I met the media-wary Pen outside the Forest Inn, a picturesque Dartmoor pub close to the Hexworthy home he shares with his wife Mary and their two young children, Wilf and Freya.

It had been just over a month since the resolute 47-year-old returned from the North Pole with fellow Devonian and polar explorer Ann Williams and adventure photographer Martin Hartley.

The team spent 73 days in the Arctic, enduring freezing, bone-chilling conditions, to measure the thickness of the ice cover and help scientists understand the impact of global warming.

Pen was now settling back into normal life: "When you get back, simple things become very difficult.

"You struggle to tie your shoelaces because your fingers have lost sensation. Everything has changed on a physical level. You are used to dealing with big things."

In the extreme cold and white wilderness of the Arctic, a cup of hot tea, poured from a thermos flask into a cup freezes in 10 minutes.

Sleeping bags and clothes freeze and, when the temperature does rise, everything is left soggy.

Temperatures can plummet to minus 40 degrees and there's no official time zone in the largely uninhabited region which lies in darkness for most of the winter.

"If you imagine a fridge is five degrees Celsius and a freezer is minus 15, we were operating for days without respite in temperatures two or three times colder than the deep freeze.

"Although I had been there before, I wasn't able to hold the memory of just how uncomfortable, in an almost surreal sense, it really is.

"When you're warm, at home, you can tell yourself how awful it's going to be, but when you get here, the shock of it hits you all over again and you really can't believe you've allowed yourself to go through it again.

"It slows the brain up and it's unbelievably difficult to communicate and make movements at below minus 30 or minus 35 degrees Celsius."

The team had to drag sledges weighing up to 19 stone carrying equipment, food and shelter across the Arctic while still finding energy to carry out the survey, which involved drilling holes into the ice and measuring the thickness and temperature.

"You are trying to perform at a far higher level than you are in normal life and yet you are 'drunk'.

"It's as though you have consumed a litre of whisky and you are driving down the motorway at high speed.

"Something is going to go wrong — but it mustn't go wrong because if it does, it compromises the project."

"There is this constant tension, but the harder you push yourself the more likely it is someone is going to fall through the ice and get frostbite.

"You are pushing yourself to the edge, and that's where I like to be. That's what it's all about."

Pen was brought up in the Scottish Highlands where his taste for adventure began with a 'polar conditioning programme' overseen by Nanny Wigley. She had been nanny to Scott of the Antarctic's son Peter, then to Pen's father and finally to Pen himself.

Scott's widow had instructed Wigley to toughen up her offspring. He was encouraged to play outside in the snow wearing little more than a pair of shorts and a shirt.

Years later, Pen underwent the same programme which was only terminated when a friend of the family pointed out that he was suffering from frost-nip.

Wigley continued to fill Pen's head with tales of Scott and the 'Antarctic boys', fuelling an almost congenital passion for adventure.

While at London's Harrow School Pen became the first pupil in 50 years to take up the tradition of Long Ducker, a marathon run from Harrow-on-the-Hill to Marble Arch and back.

I get the feeling Pen would be the first to admit the unsettling nature of being so focused and unwilling to accept defeat.

It was this unrelenting drive which brought about Pen's first major achievement. In 2003 he became the first person to reach the North Pole, having walked alone and without re-supply the 480 miles across the Arctic Ocean from Canada — comparable to climbing Everest solo and without oxygen.

It had taken two failed attempts and 15 years of determination.

On the third attempt, he fell through the ice and almost drowned. He lost a ski and had to complete the last 150 miles on foot suffering severe hypothermia.

Media reports had wrongly suggested his life was at risk and as a result his family found themselves at the centre of an unwanted media frenzy.

The feat, which pushed him mentally and physically to the very edge, catapulted Pen to international fame and earned him a place among the greatest explorers of our time.

At the time he told The Times: "I gave my father an undertaking shortly before he died in 1993 to make it to the North Pole solo and with no re-supply, and to have completed that is everything to me. This whole expedition has been dedicated to his memory and so I am very, very pleased.

"It's the end of one journey, but having put so much time and effort in for so many years, I realised with my last 10 steps to the Pole that I couldn't have closure just like that."

Just eight months later he trekked to the South Pole unaided and without re-supply.

In 2004 Pen's first book Solo was published about his experience on the ice. The book reveals the inner turmoil he felt at needing to complete this unprecedented task and leaving his wife and young children behind.

At about the same time Pen started to plan for the Catlin Arctic Survey.

"I have always been driven. I said to myself I would know when I came back from my solo project if I could relax and be a tree surgeon or something.

"I now know I am hard-wired to strive to do the best I can in whatever field — it's not always a comfortable thing for people around me.

"But success can, more often than not, come at a price for one's social and private life.

"Mary has been very supportive because it's not easy. We live out in the sticks on the high moor with young children.

"Mary is remarkably self reliant and has always been encouraging. She has never tried to manage me into a nine-to-five way of life.

"The children reacted to the expedition with a mixture of pride and concern, but I think I convinced them of the difference between going alone and going as part of a team."

As part of their preparation for the survey, the team underwent rigorous physical training on the moor with Jon Stratford, a former fitness instructor at the Royal Marines Commando Training Centre in Lympstone.

The team also had sessions to help prepare them psychologically with Dr Mark Wilson from the Sport and Health Sciences Department at Exeter University.

The team had to be physically able to haul their heavy sledges over jagged pressure ridges and broken terrain for days on end.

"Jon got us to do quite a lot of intense, if not extreme, exercise but as a three. It built up our physical confidence and hardness as a threesome.

"There was always one who was really in pain. He was very clever at getting us to work as a team and support each other."

At one stage the team were tent-bound on emergency rations for 10 days as poor weather prevented the supply plane landing.

"The long wait was very hard. We spent a lot of the time sleeping once we became unable to do anything on the survey front.

"Being very hungry, cold and without hot food has few redeeming features but we did kill the time quite effectively. Mostly with a series of rather intense conversations."

Fortunately they emerged relatively unscathed.

"The only significant injuries were to Martin's toes. His big toes were severely frostbitten and he was in a world of pain for more than 40 days and wasn't able to think about anything else.

"He never gave up and it was inspirational. There was no chance of feeling sorry for yourself with Martin at your side."

But the source of greatest anxiety for Pen was gathering data and information about the sea ice thickness.

"No one has ever done it before as part of a specific expedition. We knew we could travel for a long period, what we didn't know was to what extent we would be able to survey. We found what the balance was and how far we could travel for the day and leave enough time to do the survey."

The team took about 1,500 specific measurements. The results were worrying.

Where the ice is 2.5m or thicker, it's known as multi-year ice, which has already survived an Arctic summer.

Fewer than one per cent of the measurements the team took showed the presence of this older, thicker ice.

The data they have collated will be studied by organisations including the US Navy, the Met Office, University College London, The EU Space Agency and the University of Alberta.

The findings will be taken to the national negotiating teams working to replace the Kyoto Protocol agreement at the UN Climate Change Conference in Copenhagen in December 2009.

"Our data will be presented to a committee of 40 different organisations. Our accurate measurements will help them to see to what extent their models are near the reality.

"In 20 to 30 years from now the ice caps could be a seasonal feature.

"So much is going on up there and it's changing so fast. New shipping routes are opening up and oil and gas is being revealed as this protective ice is melted away. There is big business and international interest in the Arctic.

"People need to know about this. It's not some obscure place. It will result in habitat loss and certain flora and fauna which depend on the sea ice for existence.

"This goes right up the chain to polar bears. All eyes will look north — I really believe that."

Pen's ambition has become much bigger than him. His responsibilities have grown. He is an environmental spokesman, warning us about the dangers of global warming from firsthand experience.

He isn't an armchair scientist with a computer program — he really is the thinking man's explorer.