Detectives from Scotland Yard arrived in Moscow two weeks ago to interview several Russians who met with Litvinenko before he died last month in London from radiation poisoning.
The British investigators were not allowed to question the witnesses themselves, but were present when Russian prosecutors interviewed them.
The Prosecutor-General's Office said in a statement today the British investigators were given "complete and all-round assistance."
It said the British investigators were given an array of material, including transcripts of the interviews with the witnesses.
It was not immediately clear when the British investigators would return to Britain.
(compiled from agency reports)
