Britain has identified Russia [Images] as the third most serious threat to its internal security.

Security sorces say only the the Al-Qaeda [Images] and the Iranian nuclear programme rank higher than the Russian threat.  These facts have emerged just before British Prime Minister Gordon Brown's first meeting with the new Russian President Medvedev.

The British secret services believe that the Russian spy agencies have flooded Britain with fifth columnists. The services are also deeply dissatisfied that crucial resources are being diverted to fight the Russian military and industrial espionage.

Russian agents are suspected to have murdered their ex-agent Alexander Litvinenko in London [Images] and are also accused of harassing the staff of British Petroleum in Russia.

As Brown and Medvedev prepare to meet in Japan [Images], before the opening of the G8 summit, Russia has shown signs of wanting to end the rift with Britain.

Medvedev, while talking to reporters, said that international relations always required people to come together. Senior British officials refused to give details about the issues that Brown intended to raise in the meeeting. Sources said  Brown looked forward to a constructive discussion .

Relations between the two countries had deteriorated very badly, with a row between British Prime Minister Tony Blair [Images] and former Russian President Vladimir Putin [Images] at the last G8 summit. There is also the issue of long range flights by Russian aircraft which violate North Atlantic Treaty Organisation airspace.

Image: Russian President Dmitry Medvedev at the Kremlin in Moscow [Images].

Photograph:Dmitry Astakhov/AFP/Getty Images