So we wait for him in a chateau outside Paris. Gorbachev has stopped off here, en route from America to Moscow, partly to give this rare interview. First, we are told, he must rest. An aide hints at health problems, but Gorbachev, when he appears, looks almost unaltered.

The hair combed back from his signature birthmark is greyer and his waistline plumper than when he impressed Margaret Thatcher as "a man I can do business with". Even so, the aura of power remains as palpable as the air of loss.

Almost 10 years have passed since the death of his wife Raisa, and he misses her bitterly. "It is still difficult for me," he says. "We met when we were hardly more than children, and we lived through so many dramas, joys and tragedies. Raisa died just four days before what would have been our 46th wedding anniversary. We were so happy together."

A few weeks from now, Gorbachev will visit Britain for a glittering fund-raising dinner at Hampton Court in aid of the charitable foundation he set up three years ago in her name. A previous event at the same venue raised £1.8 million from 500 guests, including J.K Rowling, Naomi Campbell and Sir Elton John. advertisement

Gorbachev, the communist who came in from the cold, has beguiled the rich West, just as Raisa once did with her warmth and haute couture wardrobe. But that is not what her husband remembers most. Her foundation works for children who contracted leukaemia after the Chernobyl radiation disaster, and he still recalls her devastation at their plight.

"In a small Russian hospital, she met young mothers with their babies. These women were on their knees, weeping and pleading for help." Soon afterwards, Raisa herself was diagnosed with a rare form of leukaemia. Her death, at 67, surprised no one.

Her vibrancy had faded from the day, in August 1991, that the Gorbachevs were held prisoner in their Black Sea holiday home after a coup against the regime as the Soviet Union crumbled. The uprising was quelled, but Gorbachev's tenure was effectively over. Raisa never recovered from the ordeal, suffering a series of strokes before her final illness.

While he blames his successor, Boris Yeltsin, Gorbachev is also crushed by guilt. He has hinted in the past that his crusade for glasnost and perestroika - openness and reconstruction - cost his family dear.

Now he admits to personal guilt over his wife's death. "I really do blame myself. I paid too heavy a price for perestroika. Raisa was so sensitive, and when the Yeltsin team started a campaign of slander, she took it too close to her heart. They wanted to attack me through my family; my vulnerable spot."

I expect Gorbachev to recount a fairytale marriage, in which he, the grandson of a peasant farmer, fell in love with the railway worker's daughter who became a sable-clad First Lady able to entrance the West (with the notable exception of Nancy Reagan, who never forgave her for not looking like a hod-carrier).

But although Gorbachev has previously said that he and Raisa discussed "Soviet affairs at the highest level", he admits for the first time that she loathed and resented politics. "Raisa did not take part in big politics; she felt politics was stealing her husband away from her.

So she didn't like it very much. She saw what the political situation was doing to me, and she was sad because she saw how bad I was feeling.

"Often we would discuss which of us was the more lucky in marrying the other. She died before we found an answer.

"Sometimes, people would ask Raisa the secret of why she looked so young and beautiful. I would chip in and say it was because she was fortunate enough to be married to me."

Even to Gorbachev, the joke must have sounded thin. I had assumed that God had helped to assuage his guilt and made him feel closer to Raisa, a woman of deep religious conviction.

It was reported only last month that he had finally declared himself a Christian, following years of speculation about his faith, after praying at the tomb of St Francis of Assisi. Ronald Reagan, who thought Gorbachev "a closet believer", had apparently been proved right.

But, far from being resolved, the mystery of Gorbachev's faith has deepened. He is, he tells me now, a fervent atheist. "There was much ado about my visit to the monastery. I have deep respect for believers.

Raisa's father was a diehard communist, and her mother prayed to God. You could be expelled from the party for religion, but they had an image of God in one corner and, in another, portraits of Lenin and Stalin. I have vivid memories of that room. But I personally am an atheist."

At first I think this must be a translator's slip. (Gorbachev speaks no English, at least in public.) But he repeats: "I say again that I am an atheist. I do not believe in God.

" Baptised into the Russian Orthodox Church, he long ago renounced that credo. He has, however, always fervently opposed the suppression of religion. "The revival of faith was very important for our country," he says.

If negative on God, then Gorbachev tests positive on Mammon. Even by the standard of Western leaders (let alone the dour patriarchs who preceded him), he has raised the benchmark of bling.

The gaudy Russian cultural centre where we meet sits among beech trees in classically French parkland, but the Doric columns and swagged drapes evoke a stage set for a Chekhov play. His billionaire Russian friend, Alexander Lebedev, and Lebedev's son Evgeny, are here with him.

Gorbachev has promoted Raisa's foundation at both Hampton Court and Althorp, formerly the home of Diana, Princess of Wales. Raffle prizes have included a cabbage, herring and vodka lunch with Gorbachev, for which one US couple bid $160,000.

No doubt they considered it good value, for he is charming company, and as sharp as ever. He is also happy to mingle with fellow celebrities from Simon Cowell to Salman Rushdie.

As well as endorsing Pizza Hut, he recently became the face of Louis Vuitton luggage, following in the Louboutin-shod footsteps of Scarlett Johansson. "I am a kind of celebrity. I run my own foundation [the Gorbachev Foundation] using money I earn myself.

Ex-Presidents of the United States get state subsidies. Not so in Russia. You get no government support."

He says he had to build a new headquarters after Yeltsin took away his foundation building. "That's why I agreed to advertise Pizza Hut." Louis Vuitton, he suggests, helped him bankroll more charitable work. "I am doing it in an open manner. The press jump on it, but what's to be done?

"You know what my pension is from the Russian state?" he grumbles. "$1,000 a month [around £500]. My granddaughter Anastasiya has a job now, and she is getting a bigger salary than me."

The Gorbachevs had one daughter, Irina, the mother of Mikhail's cherished granddaughters, Kseniya and Anastasiya, who are in their twenties and regulars on the international party circuit.

But Gorbachev is not frivolous at heart, and nor was Raisa. "I have always wanted to be in the land of Hobbes and Locke," she once remarked to a startled British Cabinet minister, who could bring to mind no equivalent Russian cultural lodestars.

Her husband has two great regrets. The first is that nuclear non-proliferation, for which he won a Nobel Peace Prize, has stalled. "Political leaders still think things can be done through force, but that cannot solve terrorism. Backwardness is the breeding ground of terror, and that is what we have to fight."

His second sorrow is the absence of Raisa. "I turn to her in my memories," he says. "I take force and power from them." Before he left Moscow on his latest trip, he stood at her grave in the Novodevichi cemetery.

"I went with all my family, and we took flowers. We spoke about her, and I felt peace, calm and strength. I would like her to know that she is still loved the way she was loved when she was alive."

Is he afraid to die? "No, I do not fear death. If God exists, I have respect for him. I am grateful to my parents who gave me the genes to live until 77; quite a big age." But Gorbachev, despite this late admission of a shred of faith, has discarded any hope of an afterlife. Instead he hopes to stave off mortality for as long as possible.

"We have a Russian song, which goes like this: 'Old age will not catch me at home; I'm always on the move; I'm always on the road.' This is one more stop on my journey." And he is gone. Mikhail Gorbachev, still fighting time, remains one of the few world leaders who could make the world spin faster on its axis.