Tens of thousands of Russian spies are living in Britain, a major report which has been endorsed by the former head of MI6 has warned.

A new study from the Henry Jackson Society thinktank said there were as many as 75,000 informants in London - half the 150,000 Russians who live in the capital - who are actively helping Moscow's secret service.

The study also warned of a huge increase of Russian case officers in the UK over the past eight years, with 200 officers handling an estimated 500 agents.

And the report estimated that as many as half of Russian Embassy diplomats are actively engaged in intelligence work.

The report said the number of spies now comfortably outstrips Cold War levels. Oleg Gordievsky, the KGB colonel who was a double agent for MI6, estimated there were 39 Soviet case officers in 1985.