'I never thought he would die'

It reads like a spy novel - ex-KGB agent defects to England and six years later suffers a slow, agonising death when a lethal radioactive isotope, polonium-210, is slipped into his tea. Alexander Litvinenko's story has already been made into a film that premiered at the recent Cannes Film Festival, while Hollywood movie-makers have bought the rights to a new book about the case.

But this is not fiction - and little more than six months after his death, his widow, Marina, 44, is trying to maintain as much normality as she can for the sake of their 13-year-old son, Anatoly.

At the recent G8 summit, Tony Blair had private talks with Russian president Vladimir Putin to urge him to extradite the chief suspect, former KGB officer Andrei Lugovoy, to stand trial in the UK. Putin has so far refused and Lugovoy maintains his innocence. The politics will continue, but for Marina and Anatoly life must go on.

Anatoly is coping surprisingly well and is being strong for his mother, she says. ''He doesn't like to show his experiences because he's afraid. He tries to be cheerful.''

When her beloved Alexander, or Sasha as she called him, fell ill after a meeting with two Russians at the Millennium Hotel in London last November, at first he thought he had food poisoning.

For the first few days Marina nursed him when he was being violently sick at their home in North London. Little did she know she was opening herself up to contamination. He had been poisoned with polonium-210.

The amount he had received was equal to about 100 lethal doses, or the equivalent of being in the epicentre of the Chernobyl catastrophe twice. Casualties of Chernobyl lasted two weeks. Alexander was a fighter. He survived for three.

The man who just days before had been fit, healthy and positive just faded away as the tiny nuclear explosion inside him did its worst. He died at University College Hospital, London, on November 23, aged 43.

It took two weeks to release his body for the funeral because of the environmental hazard. The body was finally released to the family in a special, sealed casket. If they want to cremate him they'll have to wait 28 years, until the radioactivity decays to safe levels.

''I never thought he was going to die,'' says Marina. ''Even when they said he had a 50:50 chance, even up to the very end. I kept telling myself it was just another crisis. It's still quite strange for me that I live, but he's not here. His last words to me were, 'Marina, I love you so much'.''

Marina is still campaigning for justice and hopes that Death Of A Dissident, a book about her late husband that she co-wrote with their friend Alex Goldfarb, will keep the issue in the spotlight.

Her tears flow freely when she recalls her beloved Sasha. ''He was the person I knew made up my other half. We had different interests in business and in life, but we knew we were made for each other.''

They met in Moscow through friends, on Marina's 31st birthday in 1993. She was divorced and he was unhappily married with two children. A week later his wife kicked him out and they slowly and shyly began courting.

He would turn up on her doorstep unexpectedly with flowers, then vanish for a few days, then appear again without warning to take her out.

Alexander quickly moved in with her in Moscow and, after four months, Marina was pregnant, a wonderful miracle as she had been told by doctors that she had a fertility problem.

As far as his work was concerned, it seems that Marina looked the other way. She created a home for him and their son away from the mobsters, racketeers and corruption he investigated.

She says now that, at first, his job with the FSB (formerly KGB) wasn't dangerous, more inconvenient. He could be gone for days, be called at all hours of the day and night. ''He was very responsible for everything he did. I supported him even though it was difficult for me at times.''

But she always sensed he had a harder side to him that he tried not to show her. When he planned their escape from Russia, Marina didn't know what was going on until the last moment. When he finally told her, there was no time to argue.

Alexander turned whistle-blower in 1998, denouncing corruption at the FSB and exposing an order to kill billionaire businessman Boris Berezovsky, his one-time employer. He spent nine months in prison awaiting trial on charges of abusing his office, but was acquitted and fled to Britain in 2000, where he claimed political asylum.

It was a huge shock for Marina, she recalls. But she found it surprisingly easy to adapt to life in England. ''Everybody was very helpful. I didn't feel lonely or isolated, although at first I missed all my friends.''

Once the family was settled, Alexander continued his campaign against his former employers. At the time of his death he was investigating the murder of the journalist Anna Politkovskaya.

Today, Marina lives in a safe house in the Home Counties. She has no bodyguards, although she does have closer contact with Scotland Yard than most citizens. ''Sometimes officers asked me to be a bit more vigilant, but I've never been scared.''

Polonium is harmless unless inhaled or swallowed. After her husband's death, Marina took one test which showed a positive result for ingesting polonium. Doctors say she has a slightly higher risk than normal of cancer in the long term.

Anatoly, who had much less physical contact with his sick father, has been given the all-clear.

Meanwhile, their home in North London is still closed because no one will stump up the thousands of pounds needed to decontaminate it.

Marina says: ''Sasha's death has changed my life completely, but I work hard to save some part of my normal life, to take Anatoly to the cinema, meet my friends, and that's some compensation.

''Sasha charged me so much that I just continue running on that energy as if we are still wired to each other. I don't think it will ever stop.''

Death Of A Dissident, by Alex Goldfarb with Marina Litvinenko (Simon & Schuster, £18.99).