Allegations by the Russian government that British agents have used a high-tech rock as a spying tool have refocused attention on the world of international espionage.
Melita Norwood was exposed as a spy when she was in her 80s
BBC News looks back at the spying cases which have shaken ties between the two countries over the years.
Melita Norwood, the Soviet Union's longest-serving spy in the UK, was exposed when a KGB archivist, Vasili Mitrokhin, defected to the West in 1992 with a list of agents.
She had worked for the Non Ferrous Metals Research Association for over 30 years, a position from which she passed on vital secrets about Britain's nuclear weapons programme. She was decorated by the KGB for her work.
Mrs Norwood, who was in her late 80s when she was exposed, was never prosecuted and lived in south London until her death in 2005.
Oleg Gordievsky was one of the most senior KGB officers to defect to the West. He was stationed at the Russian embassy in London from 1974 and recruited by MI6 as a double agent.
For 10 years, he passed high-grade information to his British handlers via a flat in Bayswater, but was summoned back to Moscow in 1985 as suspicion grew about his role.
He escaped across the Finnish border in the boot of a car with the help of British agents and has lived in the UK since. He went on to co-author a book, KGB: The Inside Story, on his experiences.
In 1971, ministers told Prime Minister Edward Heath that there were a least 120 Soviet intelligence officers operating in Britain. They warned that this aggressive espionage was doing considerable damage to British interests.
The resultant probe, "Operation FOOT", came to a head on 24 September 1971 when the government ordered 90 Soviet officials to leave the UK. It also revoked the visas of a further 15 officials who were abroad at the time. The Soviets retaliated by expelling 18 British diplomats.
The action proved to be a success, however, with former KGB officer Oleg Kalugin later stating that Russian espionage in the UK suffered a blow from which it never recovered, according to MI5.
Kim Philby was one of five spies recruited at Cambridge University
Perhaps the most famous case is that of what the KGB called the "magnificent five", a group of students recruited at Cambridge University.
The five were not motivated by financial gain but by the belief that capitalism was corrupt and that the Soviet Union offered a better model for society. They secured sensitive government posts from which they passed valuable intelligence to the Soviet Union.
Two, Guy Burgess and Donald Maclean, were exposed in 1951, when they were working at the Foreign Office. Both defected to the Soviet Union. Another official, Kim Philby, who had worked in senior positions both within the Foreign Office and the intelligence services, was exposed five years later.
In 1964 a former member of the intelligence services, Anthony Blunt, was named as a fourth member of the ring. The identity of a fifth member, John Cairncross, a former MI6 officer, was not confirmed until 1990.
A key event prior to the Cold War was the defection of former head of the Soviet Military Intelligence in Western Europe General Walter Krivitsky. In 1940 he gave the British government its first detailed insight into the Soviet intelligence system.
He was found dead in the Bellevue Hotel in Washington DC in February 1941 and suspicion grew that he had been murdered by Soviet agents. However, the FBI has said no information was ever uncovered to prove his death was anything other than suicide.