The Kremlin has denied that poisoned former Russian double agent Sergei Skripal wrote to Vladimir Putin asking to be pardoned.
Mr Skripal, who remains in a coma along with his daughter Yulia, has been living in the UK since 2010 after being convicted of selling secrets to British intelligence.
His old school friend Vladimir Timoshkov told the BBC on Saturday that Mr Skripal phoned him in 2012 and said he wanted to be allowed to visit Russia.
The Russian Embassy has since denied that claim, writing on Twitter: "Kremlin spox: there was no letter from Sergei Skripal to President Putin to allow him to come back to Russia."
Mr Timoshkov said he lost touch with Mr Skripal after they left school, but that he had contacted Yulia when her father was imprisoned for treason.
He told the BBC: "In 2012 he called me. We spoke for about half an hour.
"He called me from London. He denied he was a traitor."
Mr Timoshkov added that Mr Skripal told him that "he wrote to Vladimir Putin asking to be fully pardoned and to be allowed to visit Russia. His mother, brother and other relatives were here".
He added that his friend "regretted" being a double agent "because his life had become all messed up".
Mr Skripal, 66, and his 33-year-old daughter were poisoned with the nerve agent novichok in Salisbury, Wiltshire, on 4 March.
Theresa May and European Union leaders have blamed the Russian state for the attack but Moscow has repeatedly denied any involvement.
The incident has caused a major diplomatic row, with the EU recalling its ambassador to Moscow and several EU countries set to follow Britain's suit in expelling diplomats it believes are posing as spies.
Russia responded by expelling UK diplomats and shutting down the British Council cultural organisation.
Moscow's denial of the letter comes as Russia's ambassador to the UK wrote to Detective Sergeant Nick Bailey, who was recovering in hospital after being exposed to novichok whilst investigating the case.
Alexander Vakovenko wrote: "I would like to express my sincere gratitude to you for your bravery when reacting to the assault on two Russian nationals, Sergei and Yulia Skripal, on 4 March in Salisbury, who I hope will get well soon too.
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"Please be assured that Russia has nothing to do with this reckless incident and is ready to co-operate with the British authorities with regard to the investigation both bilaterally and through international organisations."
The bench that Sergei and Yulia Skripal were sitting on when they were discovered unresponsive in Salisbury was taken away for analysis on Friday.