Russia seeks UK Litvinenko probe

The "commission rogatoire" - a legal instrument allowing co-operation between foreign countries - was sent to Home Secretary John Reid.

The Home Office confirmed a request had been made from the Russian authorities.

The UK investigating authority, in this case the Metropolitan Police, said a decision would be made "in due course".

'Likely poisoner'

Mr Litvinenko, 43, died in London in November after being poisoned with radioactive polonium-210.

His friends have accused the Kremlin of ordering his assassination in response to his criticism of President Vladimir Putin, but the Russian government has rejected such claims.

A Home Office spokesman said: "The Home Secretary has not agreed to any specific request from the Russian authorities.

"The home secretary considered the general request for assistance and passed the request to the appropriate police authority, who will ultimately make the decision as to whether, and in what form, the assistance might take."

Police sources have told the BBC that the "most likely poisoner" was former KGB officer Andrei Lugovoi, who met Mr Litvinenko in London on the day he fell ill.

Mr Lugovoi said he had been a victim of radiation poisoning himself.

Last Wednesday, Scotland Yard handed a file on its investigation to the Crown Prosecution Service.

A Metropolitan Police spokeswoman said: "When a request for mutual legal assistance is received, the matter is considered and a decision is made in due course."