A police spokeswoman said the man was arrested in London on June 21, and was handed over to immigration officials two days later.
Earlier on July 18, Berezovsky, a fierce critic of Russian President Vladimir Putin, told a news conference in London that British police in June had warned him about an assassination plot and advised him to leave the country temporarily.
"A month ago, officers of Scotland Yard called me and informed me that there is a plot to kill me, that there is someone who I know here, and they asked me, as quick as possible, to leave the country," Berezovsky said.
Berezovsky said he had left Britain on June 16 for a week, until police told him the plot had been foiled.
The revelations come amid high tensions between Britain and Russia over Russia's refusal to extradite the chief suspect in the radiation poisoning of former Russian security officer Aleksandr Litvinenko.
Berezovsky was among the first to accuse the Kremlin of ordering Litvinenko's murder.
Britain has repeatedly refused Russia's request to extradite Berezovsky to face fraud charges in Russia.
(compiled from agency reports)