MPs will make Britain more vulnerable to terrorist attack if they vote against the Government’s proposals to hold suspects without charge for 42 days, two of the country’s most senior former spies said last night.

In an interview with The Times, Baroness Park of Monmouth and Baroness Ramsay of Cartvale, who both worked for the Secret Intelligence Service, commonly known as MI6, for much of the Cold War, said that the country would become more dangerous if the measure were to be rejected in the Commons today.

“MPs will be very irresponsible if they take out the 42 days,” said Lady Park, who is known in Whitehall as the Queen of Spies. “They will put our lives at risk. One day something vital will turn up two days after they have released someone at 28 days.”

Lady Ramsay, a former member of the Intelligence and Security Committee, said: “There is no question there will be more terrorist attacks in future, it’s not a question of if, it’s when. Voting against 42 days increases the odds in favour of the terrorists.”

Lady Park, 86, was one of MI6’s most senior controllers for more than 30 years, with postings in Moscow, Hanoi and the Congo. She said that MPs should recognise that prosecutors needed longer to sift the evidence. “These are global inquiries . . . there is an enormous amount of material to go through . . . there is no way of making it go faster.”

Lady Ramsay, 71, was on the MI6 Iraq desk during the Gulf War. She said: “People who don’t know the oper-ational realities are being arrogant to think they know better than the people who do.”

The rare intervention by two such senior former intelligence officers on the eve of the crucial Commons vote is a clear sign that the security services are privately in favour of an extension. There has been speculation that the heads of MI5 and MI6 have reservations about the plan.

The two peers are considering attempting to reinstate the 42-day clause when the Counter-Terrorism Bill reaches the Lords if MPs reject it today. The measure would, however, almost certainly be rejected by the Upper House.

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