George Galloway has said he rejects claims Russian President Vladimir Putin was involved in the murder of Alexander Litvinenko and said a British inquiry is "riddled with imperfection".
The former MP and leader of the Respect party said the investigation was "another Whitehall farce" which relied on "secret evidence" and risked derailing the UK's relationship with Putin who is "the most popular politician on the planet".
"Large sections of this process were closed to the public," he told BBC's Newsnight, explaining he didn't accept the report "because I no longer believe automatically what the security services say."
A judge-led inquiry on Thursday concluded that Vladimir Putin "probably" personally ordered the murder of former KGB spy Alexander Litvinenko in London in 2006.
Galloway dismissed this claim and said there could be no certainty that former agents Andrei Lugovoi and Dmitry Kovtun were responsible for the murder: "This process is so riddled with imperfection it cannot be relied on. I think they are prime suspects but we've gone much further."
Referring to the radioactive material used to kill Litvinenko, he said: "I know polonium-210, I was at [former Palestinian leader] Yasser Arafat's bedside in France when he died from polonium-210 so I know how foul a murder this was."
Galloway, a presenter on the state-backed Russia Today channel, said the BBC had bought the report "hook, line and sinker" and accused Newsnight of arranging a "show trial" of Putin while noting that "spies and their associates often end up dead".
Presenter Evan Davis suggested Putin's reputation was now "in the dirt" as a result of the investigation.
"You've certainly done your best to put it there," Galloway replied. "We need Putin, who is by the way the most popular politician on the planet with public opinion poll ratings in the 80 percents."
"Like Stalin," fellow guest Alex Goldfarb interjected.
"The reality is we need Russia," Galloway continued. "Russia was very popular in the West when a drunkard who was handing over Russia's wealth to the oligarchs was in power. It's not so popular now that Russia has a strong president that is trying to restore some of the lost prestige.
"But we need Russia. We need it to fight a much bigger threat, which is the threat of Islamist extremism in Syria and elsewhere. We need Russia for the Iranian file. We need Russia for all kinds of things. We mustn't our public interest to be sacrificed to the Cold War agenda of Mr Goldfarb."