British police announced on Friday that Alex Allan, 56, who heads the Joint Intelligence Committee, was in a coma in hospital after falling seriously ill on Monday.
Although police have said there are no indications that Allan was poisoned, British tabloids have been quick to link the incident to the fatal poisoning of Russian security service defector Alexander Litvinenko in November 2006, the cause of a diplomatic row between Russia and the U.K.
The Sun cited "security experts" as saying "Alex Allan may have been an assassination target of the Russians or al-Qaeda."
The paper, along with the Daily Mail, cited "top security expert" Chris Dobson as saying: "The nature of his sudden illness, if it is an assassination attempt, points towards the FSB, successors of Russia's KGB. They are the masters of assassination by poison."
The Daily Mail pointed out that fears of an assassination attempt "coincide with a warning from intelligence sources today that Russia is now the third biggest threat to national security after al-Qaeda and Iranian nuclear proliferation."
However, broadsheet The Daily Telegraph cited a government source as saying assassination theories have little basis.
Allan is "so high-profile that he would be a very unlikely target for attack. He is a civil servant and he doesn't have enemies. There is no reason for him to be targeted by anyone," the source told the paper.
British media quoted the country's security service on Friday as saying that Russia has flooded the country with secret agents in recent years, making the Kremlin a major menace to national security. The reports come days before Prime Minister Gordon Brown's first meeting with Russian President Dmitry Medvedev at the Group of Eight summit in Japan, set for July 7-9.
