British police confirmed Wednesday they had arrested a man on suspicion of conspiring to murder Russian tycoon Boris Berezovsky — a Kremlin critic and friend of the poisoned KGB agent Alexander Litvinenko.

The Metropolitan Police said they arrested the man in central London on June 21 and handed him over to immigration officials two days later.

The revelation came as Britain said it would not accept a trial in a third country of Andrei Lugovoi, a former KGB agent accused of using radioactive poison to kill Litvinenko.

"We want the trial to be in a British court, on British soil," said Michael Ellam, spokesman for Prime Minister Gordon Brown.

The spokesman earlier said only that the trial should take place in a British court — raising the prospect of a hearing in a third country.

Brown's Downing Street office said any confusion was unintentional and stressed it was seeking a trial in Britain.

Britain this week ordered four Russian diplomats to leave the country because of Russia's refusal to extradite Lugovoi, named by British prosecutors as the chief suspect in the killing of Litvinenko who was poisoned with a radioactive isotope in London in November.

Russia has threatened unspecified measures in response, leading to concerns that both sides are taking extreme positions that could make resolution of the dispute difficult.

Berezovsky, a one-time Kremlin insider who has fallen out with Russian President Vladimir Putin, said Wednesday that he fled Britain briefly last month because British intelligence services told him his life was in danger.

"I was informed by Scotland Yard that there was a plot to kill me, and they recommended to me to leave the country," Berezovsky told The Associated Press. He said he left Britain for about a week and returned when Scotland Yard told him the plot had been foiled.

Berezovsky was granted political asylum in Britain in 2003. His visibility has increased since Litvinenko's murder.

Scotland Yard confirmed Berezovsky's claim, saying they had arrested a man on suspicion of conspiring to murder the tycoon on June 21. Police said the suspect was handed over to immigration officials two days later.

"Berezovsky is a very high-profile critic of the Putin regime, and history does show that it would appear that the Russians are prepared to take action against their critics abroad," said a MI5 domestic intelligence agency official, who demanded anonymity to discuss sensitive intelligence work.

The official could not say whether British intelligence services believe Russia has tried to attack dissidents in London since Litvinenko's murder. But the official confirmed about 30 Russian spies are believed to be based in London to monitor exiles in the city.

"I am happy that British are very strong in protecting people in this country," Berezovsky said on BBC television.

"It's absolutely useless to fight against a state alone. I don't have any chance to be alive if not for the protection of the state which gave me asylum," he said.

Russian Ambassador Yury Fedotov told British Broadcasting Corp. radio said the alleged plot to assassinate Berezovsky was "quite strange information, and I have nothing that could confirm it."

He alleged that Berezovsky is linked "to many criminal international schemes of money laundering, corruption and organized crime."