"Even if (British special services) hadn't done it itself, it was done under its control or connivance," Andrei Lugovoi told a news conference.
Later, asked if he had evidence for the allegation, he said "I have evidence" but did not elaborate.
He was not clear about what he regarded as British motivation, but suggested Litvinenko may have been trying to blackmail another Kremlin critic, tycoon Boris Berezovsky, who was granted British citizenship. He said Litvinenko may have held evidence that the tycoon received political asylum under false pretenses. Russia has long sought Berezovsky's extradition to face charges of financial crimes, which Berezovsky contends are politically motivated.
Lugovoi alleged that Berezovsky and Litvinenko were working for MI6, Britain's foreign intelligence agency.
Lugovoi also claimed that Britain had tried to recruit him to provide intelligence.
British special services "asked me to collect compromising information on President Putin," Lugovoi said.
Lugovoi said the attempted recruitment occurred during business trips to Britain in previous years. He did not give a precise date, but indicated the alleged approach occurred in late 2005 or early 2006.
Describing one piece of his alleged evidence against MI6, Lugovoi said he had been given a cell phone with to communicate with London from Moscow.
"I was instructed to collect information regarding a government official through whom they expected to collect information compromising the president (Putin). In particular, they planned to lure this official to London to get information compromising the president in exchange for silence about his personal bank accounts," Lugovoi said, without naming the government official he was allegedly told to target.
Lugovoi added: "I cannot call myself an ardent supporter of President Putin, for which I have my personal reasons… But I was taught to defend my country rather than betray it."
The British Foreign Office declined comment on the recruitment attempt allegation.
Britain last week said it had enough evidence to charge Lugovoi, who also worked for the KGB and its main successor agency the FSB, in the November killing of Litvinenko, who died of poisoning by the rare radioactive isotope polonium-210.
Litvinenko had fled to Britain several years earlier after becoming a strong critic of the Kremlin and received British citizenship. He co-wrote a book claiming that the FSB was behind the 1999 fatal apartment bombings that Russian officials blamed on Chechen separatists.
Lugovoi and another Russian had met in London with Litvinenko on Nov. 1, the day Litvinenko said he became ill.
Britain has requested Lugovoi's extradition, but Russia has refused, saying the constitution does not permit such extraditions.
Lugovoi has repeatedly asserted he is innocent in the matter.