The end of the Cold War has meant that while fewer agents are likely to betray their country for ideological reasons, more are likely to do so for money.
The findings of a House of Commons committee suggested that all three intelligence services - MI5, MI6 and GCHQ - have had to withdraw security clearance from staff and contractors because they were in debt.
The annual report of the all-party Intelligence and Security Committee says that Aldrich Ames, the CIA man who acted as a double agent for the KGB and whose activities led to the deaths of several of his colleagues, underlines the need for vigilance. Ames used much of the $3m (pounds 1.9m) he was paid by the Russians to fund his second marriage to a shopaholic who was found to have 500 pairs of shoes. The committee warns that British agents must be watched constantly.
Tom King, chairman of the committee and former secretary of state for defence, said there was no reason to believe that a British Aldrich Ames was operating undiscovered.
"There is absolutely no evidence at all that there is any question of a similar traitor working within the British intelligence agencies, but the lesson to learn from the tragic and really awful experience in the US ... is that no country can afford to sit back and assume that everything is all right," he said.
Ames, who was tried for his activities in 1994, caused ninecolleagues to be executed and a further three imprisoned, and the House of Commons committee says the fall-out from the case has not yet stopped.
Its report says that in addition to staff being vetted when they join, their circumstances should be randomly checked throughout their service.
It also warns of the risks of other countries using their intelligence agencies to gain commercial advantage over Britain. In one recent case, the US State Department advised some of its companies not to exhibit at the Paris Air Show because of fears of espionage, and John Major had asked the committee to look into the problem in this country. However, it concluded that Britain's agents were protecting its interests.
"The security service works both to counter the real and continuing threat to UK economic interests, and to provide protective security advice and assistance to government and direct to industry," it says.
The report also complains of a severe recruitment problem at the GCHQ listening station in Cheltenham, Gloucestershire. Staff trained in information technology are increasingly difficult to find and even harder to keep, it suggests. GCHQ has been paying below the market rate for its staff and will have to pay more in future.Reuse content