Mr Karpichkov, a Latvian, is facing extradition accused ofstealing $500,000 (pounds 310,000) from a failed bank in Riga, Bank Olympia. He denies this, saying the real reason he is wanted is that he uncovered corrupt links between senior figures in the Latvian government and the Russian mafia. Mr Karpichkov says that if he is sent home he will be killed. He says the mafia has taken out a $800,000 contract on him and his family.
Sixteen months ago he fled to Britain with his wife and two sons aged 13 and 16, claiming political asylum. They used false passports issued by the Latvian secret service.
A week after arriving in Britain he was arrested by Scotland Yard at the request of the Latvian government and has been held on remand. He has gone on hunger strike toraise awareness of his case.
The former major, who has limited English, said: "My family and I can't go back to Latvia or Russia ever again. If we will return, it would mean for us only death. We lost all our property, everything we had in Latvia. We do not receive in Great Britain any help or benefits because British authorities refused us."
Mr Karpichkov said he was given details about the mafia contract. "They have approached former officers of the KGB's top secret unit Alfa, who specialised in assassination. At the present time these people are looking for our family everywhere and sooner or later will find us in Britain," he said.
Mr Karpichkov, of Russian extraction and nationality, was recruited by the regional KGB in 1981 when Latvia was part of the Soviet Union. He said he was trained in the Higher Secret Services School in 1985 and as a special forces operative during the war in Afghanistan.
While working as a counter-intelligence officer, Mr Karpichkov's job was to counter US Central Intelligence Agency operations in Latvia.
In early 1990, after the Cold War ended, he was assigned to the new Russian intelligence service, the FSB. It was sensitive work investigating corruption in Latvia involving prominent political figures and key people in the Russian and local mafias.
From 1993 he worked undercover running a commercial information agency. But Mr Karpichkov was actually gathering information on money laundering through Latvia's biggest commercial banks, including Bank Olympia. The bank handled a number of International Monetary Fund credits worth millions of dollars intended for the country's industrial and agricultural development. Mr Karpichkov said that in this period he gathered an "explosive" dossier, with tape recordings, about "the close connections between highest level officials of the Latvian state with leaders of organised crime".
Mr Karpichkov said he passed some of this information to his bosses in Russia's secret services. At this point, he said, they betrayed him and told the Latvian police about his work. He said this led to his arrest by the Latvian police and later by the Russian police. He said he was tortured and beaten.
When Olympia Bank failed in 1995, questions were asked about where large sums of money had gone. Although he was not seen as a central figure, Mr Karpichkov was accused of involvement with theft. He denies the allegations. He met the attorney-general of Latvia, Janis Skarstins, in 1996 and was offered a deal under which he would have been treated as a special witness in return for handing over evidence.
Although Mr Karpichkov handed over documents and tapes, the deal fell through and he was placed under house arrest. But he escaped from his sixth-floor apartment by climbing down a rope made from knotted-together clothes, and fled with his family to Cyprus. Later they flew to Russia, and after meeting problems there they sought asylum in Britain.
Mr Karpichkov said he explained his predicament to the Home Office as part of his asylum claim, which was being processed normally until his arrest. The family were found housing by a local authority. They appear to live in poverty, dependent on hand-outs.
"The Latvian authorities only asked for extradition after I gave interviews to the Latvian press on the phone," said Mr Karpichkov. He believes they only want to extradite him to stop him publishing information abroad on corruption in Latvia.
Establishing the truth of Mr Karpichkov's claims is difficult. There is no doubt that much of his story is true, and a great deal of it is supported by Latvian and Russian newspaper articles. But whether he has defrauded a Latvian bank or incurred the wrath of his country's officials is harder to determine.
Latvia has an extradition agreement with Britain, but it does have problems with mafia corruption at a high level. Mr Karpichkov's case reflects the difficulties the Home Office faces in uncovering the truth of the many East European asylum cases in the years since the Berlin Wall came down.