PlayThe presence of Russian spies in Britain is undermining the fight against terrorism according to Whitehall Officials.
The distraction created by monitoring the espionage activities of President Dmitry Medvedev's agents, significantly enhances the chances of success of potential Islamist terrorist plots.
Security sources say MI5 has been stretched to the limit for the past few years.
Some sources suggest that one in five Moscow Government officials based in Britain is likely to be an agent.
Former Prime Minister Tony Blair famously rowed with Vladimir Putin over the issue at the G8 summit last year and successor Gordon Brown may bring it up the issue with Mr Medvedev when the pair meet for the first time.
The issue strained London-Moscow relations last summer, when Britain expelled four Russian diplomats after a request to extradite the prime suspect in the Alexander Litvinenko murder case was refused.
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