AFTER 40 years, William Hague’s all-consuming involvement in politics is coming to an end. At one minute after midnight last Monday, as the fixed term parliament was formally dissolved, he ceased to be an MP after 26 years representing Richmond. By May 7, after 40 years of driving, the last trappings of power will have drained away.

“Once polling day starts, I have finished,” he says, drawing out his syllables in his distinctive Yorkshire drawl. “I will not be coming back as anything.”

And so will end a career path that began when he became obsessed by politics when he was 13, memorising parliamentary majorities in the way other schoolboys were mesmerised by football league tables. At 16, he starred at the party conference under Margaret Thatcher's gaze; at 27, he was the youngest Tory MP; at 36, the youngest Tory leader, and at 40, the youngest ex-leader. In his mid-40s, he re-emerged as the youngest elder statesman, as popular for his wit as he was for his politics, and at 48, he achieved his teenage ambition when David Cameron appointed him to one of the great offices of state – Foreign Secretary.

“I'm looking forward to having a bit of freedom and time that I haven't had since I was 27 – well, I’ve never had really in my adult life because even before I was elected to parliament I was trying to be elected to parliament, so for my whole adult life I have been busy with politics,” he says.

“I’m excited on the whole because it's my own decision to leave parliament and I'm doing it to do other things. Many other things.”

These include working with Angelina Jolie to prevent sexual violence and helping Prince William stamp out illegal wildlife trade in ivory and rhino horn. He’s hoping to stay on as patron of some of his North Yorkshire charities and he’ll probably take up offers to teach as a visiting professor at universities on both sides of the Atlantic.

“I will certainly write more 18th Century history,” he says. “It's the period I feel at home in. I was led there by my interest in William Pitt – I could explain how he thought having been a young politician myself.

“The 18th Century is close enough to our time that you can reach out and touch the same tables, walls and chairs that people sat in, so you can visualise their world, but it was just before the steamship, telegraph and railway which revolutionised communication and travel and led to our very different world, so it's the nearest distant world.”

He talks about writing of his own experiences, but doesn’t have his own diary to draw upon.

“It is a pity but it is in the nature of being Foreign Secretary that you are busy right round the clock, piles of paperwork and reading every day, and therefore writing a diary is impossible,” he says, almost sadly.

He is a little guarded as to whether occupying the Foreign Office but not No 10 would have satisfied the 16-year-old who, with a shock of long light hair, shocked the 1977 conference by telling Mrs Thatcher’s government “to get out of the way”.

“At that time I wanted to be an MP and in government, and tactfully when journalists asked if I wanted to be prime minster I said perhaps,” he says.

“I was impelled into politics by the state of the country. Growing up in the south of Yorkshire, it was a pretty bleak outlook. Nearly all of my schoolfriends’ fathers worked in nationalised industries. They lived in local authority housing in big estates with no opportunity to buy their own homes, tax rates went up to beyond 80 per cent and the country was in decline, it was the sick man of Europe – that was quite radicalising in a Conservative sense. The country needed radical change of the sort Margaret Thatcher would bring.”

In the years since he was radicalised by Margaret Thatcher, he regards the Disability Discrimination Act of 1995 that he steered through when he was a minister in John Major’s government as one of his greatest achievements.

“It was a landmark,” he says, “a crucial moment in improving attitudes to disabled people, creating job opportunities and improving access to buildings. It means a lot to me looking back on my career.”

He hopes to have reformed the Foreign Office so that it is now a “confident institution”, and he regards the 2011 European Union Act as another personal achievement.

“It says that if any government proposes handing more power to the EU there must be a referendum,” he says. “It's an important change when you consider how many treaties which handed over powers have been signed in the last 30 years.”

Mr Hague wears his Euro scepticism on his sleeve – he is famous for his cufflinks with a map of the British Isles on them – but should the Conservatives put Britain’s membership to a vote, he wouldn’t seize the opportunity to say no. “My objective," he says, "and David Cameron’s objective, is that he will have a successful renegotiation (of Britain’s membership terms) and we will be able to recommend staying in."

Of his career highlights on a local level, he notes the improved main roads, the creation of a super-garrison at Catterick and the growth of rural business – unemployment in Richmond is just one per cent.

“Much of the work of an MP is the accumulation of thousands of small cases and helping people individually, and that has been the most satisfying side of it,” he says.

It seems impossible that this most personable of politicians will disappear beneath the dark waters of academia, never to be heard of again as he contemplates the 18th Century. But before he goes, he attempts history’s first draft of the last five years.

“I hope it will judge it very positively,” he says. “I'm confident it will on the economic scene. If somebody had said to us when we were negotiating the coalition that five years later there would be nearly two million extra jobs in the country we probably wouldn't have believed it.

"The scale of the economic turnaround is enormous and it is there in all parts of the country: three quarters of a million more businesses in the country, the fastest economic growth in Europe. That's why we formed the coalition – the two parties came together to reduce the deficit and right the economic chaos that Gordon Brown left behind.

"We will have accomplished that, and it is of enormous importance, so I think this is the most important election since, well..."

He stops to consult his mental history book, running through all the elections that he has studied over the last 40 all-consuming years, before concluding: "Certainly, in terms of what is at stake, since 1992."