Mr Litvinenko died after drinking tea laced with polonium 210
Almost a year after UK prosecutors recommended that a former KGB officer should be charged with the murder by poisoning of Alexander Litvinenko in London, BBC security correspondent Frank Gardner asks whether Britain is any closer to bringing Andrei Lugovoi to trial.
Locked up in a safe in a high-security area of the Crown Prosecution Service building in London is "The Lugovoi File"'.
It consists of just two lever-arch ring binders and a couple of ordinary brown A4 folders, yet its contents have already severely damaged relations between Britain and Russia.
The file contains all the evidence gathered by Metropolitan Police detectives into how Alexander Litvinenko died in November 2006 and who they believe poisoned him.
It contains highly sensitive testimonies from nuclear scientists at the Atomic Weapons Establishment at Aldermaston, and witness statements from defence experts, police officers, health officials and CCTV operators.
It has statements from hotel staff who saw the poisoned Russian with Mr Lugovoi and it contains graphics showing the trail of radioactive polonium with dates and locations circled in ink.
Mr Lugovoi claims he was also a victim of polonium poisoning
But the Crown Prosecution Service says almost none of this evidence has been submitted to Moscow, only a detailed summary contained in an extradition request, formally submitted in May 2007, for Mr Lugovoi to stand trial in Britain.
Sue Hemming, the head of Counter-Terrorism at the CPS, said: "The extradition request is still current.
"We hope that Mr Lugovoi will be returned in the near future to stand trial in this country for the allegations that he murdered Alexander Litvinenko.
"The only option available to us is to put in an extradition request and that's what we've done."
'Case to answer'
Russia has so far refused to extradite Andrei Lugovoi, who is now a Russian MP, saying it would be against its constitution to do so.
He has always insisted that he too was a victim of polonium poisoning at the time and not a perpetrator.
As long as he stays in Russia there is little chance of his coming to trial in Britain and British government officials said this month that "things essentially have not moved on".
But with still no-one brought to justice for what was apparently a shocking and high-profile murder by radioactive poisoning, the Foreign Office says there is still a case to answer.
It says the matter has been raised recently with the Russians and that it will continue to be raised until the prime suspect stands trial in this country.