This isn't right. In a trio made up of a journalist, a comfortably-upholstered actor and a man who turns 71 in a few weeks time, the older man should not be the one who is the big drinker.

Yet it is he who orders a bottle of wine for himself and the others only share one.

But then Tony Harrison has spent a lifetime doing the unexpected. Born to a working class family in Leeds – his father a baker, the family home in Beeston – he wasn't the sort of boy you would expect to find at Leeds Grammar School, where the exceptionally bright youngster won a scholarship.

Once there, he was not expected to read aloud in class, his flat, working-class Leeds vowels not something a schoolmaster wished to hear. The teacher's insistence that Harrison educate his natural accent out and pronounce the word "us" not "uz" inspired Harrison's poem Them and Uz.

He read classics at Leeds University and his first collection of poems, The Loiners, was published in 1970 to widespread critical acclaim. It was full of poems that were not supposed to be written by a decent lad, in the eyes of his parents.

"A lot of the poems were about sex and they never talked about that, so I didn't send them a copy. But one of my cousins found it in the library and brought it home and my mother read it and was horrified."

Almost unacceptably bright (he has often said that his parents wished success for him, but on a limited scale, perhaps as a schoolteacher, in order that they might comprehend it) the more sophisticated his education and the greater his success, the more he found himself alienated from the world in which he grew up. The world into which he would eventually be accepted was not initially open-armed either. When he read his poem V on TV in 1987, it caused an outcry. Riddled with rough language and expletives, it led to howls of protest from rent-a-quote MPs and the Daily Mail. Harrison wrote the poem after discovering football hooligans had scrawled graffiti on his parents' graves.

An interview a couple of years ago summed up Harrison thus: "The story of his life as a poet has been a never-ending fight-back against standardisation and class prejudice."

And here he is again, weeks away from turning 71, many years after most have opted for a life of ease in retirement, busying himself with a new play which he has written and is directing. In a rehearsal room of the National Theatre, where Harrison is leading the cast through his latest play, Fram, the writer and director enthusiastically shows off the tip of an iceberg of several years' worth of research which has been collated to become Fram.

The play, being staged in the National's Olivier Theatre, tells the story of the Arctic ship Fram – or Forward – specially built by the famous Norwegian explorer Fridtjof Nansen who, with his companion Hjalmar Johansen, made a bid on foot for the North Pole in the 1890s.

The idea for the play came to Harrison from a number of different sources, but it was recorded in the same way as all his ideas. "I always carry a notebook around with me and whenever I have an idea I jot it down. It might be something visual or a thought or a sound. I don't always know what they're going to end up being – it might become a film, or a poem," says Harrison.

"With this, I knew quite early on that it was theatre."

Harrison had known the story of Nansen for a long time, but it was filed away somewhere in the dim recess of his impressive mind.

"As a kid I was interested in Arctic exploration, so I knew his name," says Harrison. "But not much more than that."

Around six years ago Harrison came across a book in a secondhand store, which featured famous memorial speeches. One of the speeches was by the intellectual classics scholar Gilbert Murray about Nansen.

Harrison began reading up on the explorer and, with each new discovery, he found reason to write about him.

"He learned over 80 poems by heart, so that when he was out there in the Arctic for all that time, he would have them at his fingertips when he needed them. A man of science who was interested in art – that was something which interested me."

Then came the clincher.

Harrison came across the full story of what happened when Nansen attempted to sail to the North Pole. The ship stuck in the ice, and Nansen set out on foot with Hjalmar Johansen.

"These two men who really didn't like each other, who couldn't have been more different, absolutely relying on each other to stay alive, was such a dramatic story."

All of this began to ferment in the mind of Harrison and, surprisingly for someone who has always eschewed religion, the moment of crystallisation came in Westminster Abbey.

"I was in the abbey and had gone to see Gilbert Murray's memorial. The sun was shining through one of the stained glass windows and the light was moving down. It came down the wall and lit up Murray's grave," says Harrison. The poetic moment made it, unadulterated, into the final draft of the play. "My hair goes like that," says Harrison pulling his still-dark, if thinning, hair on end.

"It's a moment that happens to me often – you have to be on the look-out for it, be in a state where you are ready to receive it. I carry a monocular around with me to help me see how things might look on stage. I took it out, looked at the scene, and thought to myself, 'This is where it starts'."

For the staging, Harrison has returned once more to familiar ground – the classics and his Leeds upbringing – inspired by an unusual mixture of Greek classic theatre and boyhood trips to the theatre in Leeds.

"When I was a boy my dad took me to the theatre in Leeds and people were on stage and I just kept thinking 'why aren't they talking to me?' The fourth wall is a recent invention of theatre – in Greek theatre the audience and the actors shared the same light and there was always the acknowledgement that the audience was there. There was a sense of community."

Those of a nervous disposition need not worry – the lights will be coming down in the National's Olivier Theatre for performances – it's just that the play is full of dramatic devices such as direct address to the audience; unlike the actors of Harrison's youth, they will talk to you.

The other way of working Harrison embraces is one which sees the written word not as sacrosanct, but as a constantly evolving beast, so during rehearsals, he will change the script.

"There are many ways you can get old. You can get more distinguished," says Harrison, interrupting himself with a throaty laugh.

"Or you can become freer. I'm never going to be a national treasure, I value the position of being an outsider. A lot of people said I should be the poet laureate, I said 'f*** off'. Now all that matters is the work. All I want to do is look forward. Fram fram."

With his bottle of white and his adherence to his principles, Harrison will continue the poetic tradition and, as he approaches 71, is determined that old age should burn and rave at close of day.

Nansen's incredible journey

In 1893, Fridtjof Wedel-Jarlsberg Nansen sailed to the Arctic in the Fram, a round-hulled ship designed to drift north through
the ice.

When, after more than a year, it became apparent that Fram would not reach the North Pole, Nansen, accompanied by Hjalmar Johansen, continued north on foot.

They started on March 14, 1895 with three sledges, two kayaks and 28 dogs.

On April 8, 1895, they reached 86° 14 N, the highest latitude then attained.

The two men then started back. In June 1895, they used their kayaks to cross open water and on July 24, they came across a series of islands where they wintered, surviving on walrus blubber and polar bear meat.

In May of the following year, they started off again for Spitsbergen.

After the First World War, Nansen became involved in the League of Nations as a High Commissioner for several initiatives, including organising a relief program for the millions of Russians dying in the Russian Famine of 1921-1922.

In 1922, he won the Nobel Peace Prize.

Fram is at the National Theatre, until May 22. For more information log on to www.nationaltheatre.org.uk