Chapman Pincher: The far from glorious history of MI5

In the latest attempt to burnish its public image and diminish its aura of secrecy, MI5, the security service responsible for the prevention of espionage, sabotage and now terrorism in the UK, has embellished its website with portraits and potted CVs of its former chiefs, dating back to its pre-Second World War director general, Sir Vernon Kell.

Kell fell foul of Churchill, who sacked him in 1940. Under his replacement, Sir David Petrie, MI5 staged a superb performance against the German espionage threat. Sadly, MI5's performance against the Soviets was appalling to a degree that has only recently been revealed by Russian intelligence files. The Cambridge traitors - Philby, Maclean, Burgess, Blunt and Cairncross - gave the KGB more than 15,000 secret files. At the same time, Klaus Fuchs, Nunn May and Melita Norwood were feeding atomic bomb secrets to the Red Army's intelligence service.

Petrie was succeeded in 1946 by Sir Percy Sillitoe, who shouldered the blame when Fuchs was convicted. He was replaced by Sir Dick White, who had been brilliant against the Germans but failed against the Russians. Though deeply involved in the disastrous defection of Maclean and Burgess, White was switched in 1956 to MI6, securing his old job for his closest colleague - Sir Roger Hollis, who had cleared Fuchs and became the most controversial DG of all.

Under Hollis so many operations failed that his officers suspected he was a Soviet agent. His formal interrogation in 1969 was not revealed until 1981, when the renegade MI5 officer Peter Wright gave me the details. MI5 now dismisses the suspicions as a myth but all the relevant information so far released, by the Russians and by MI5, supports his guilt rather than his innocence.

Except for the first woman DG, Dame Stella Rimington, who shocked colleagues by publishing her memoirs, Hollis's successors have made scant public impact save for Sir Martin Furnival Jones, who helped secure the expulsion of 105 Russian spies from Britain in 1971 - from which the KGB never recovered. With counter-terrorism now the prime responsibility, the current DG, Dame Eliza Manningham-Buller, faces the toughest MI5 assignment yet.

Chapman Pincher joined the 'Daily Express' as Defence correspondence in 1946, and has written many books on intelligence, including 'Their Trade Is Treachery' (Bantam)