The recently retired head of London's police force said in a newspaper article published Sunday that at least 100 terrorists trained by Usama bin Laden are at large in Britain.

Sir John Stevens (search) also said the threat justified tough anti-terror proposals, including placing suspects under house arrest without charge, that the government is struggling to get through Parliament.

"As you read this, there are at least 100 Usama bin Laden-trained terrorists walking Britain's streets," Stevens wrote in the News of the World weekly. "The number is probably nearer 200 ... the cunning of al-Qaida means we can't be exact.

"But they would all commit devastating terror attacks against us if they could, even those born and brought up here," added Stevens, who retired as head of the Metropolitan Police last month.

Prime Minister Tony Blair's (search) government wants the new Prevention of Terrorism Bill (search) to include the power to order sweeping controls on terror suspects, including house arrest, electronic tagging and bans on using the Internet and telephone.

Critics say the bill would undermine civil rights. But Stevens said it was "vital" that lawmakers approve the new legislation, which is being rushed through Parliament (search) to replace anti-terror laws that Britain's highest court denounced on human rights grounds.

"For the safety of the vast majority, occasionally we will have to accept the infringement of the human rights of high-risk individuals," Stevens wrote.

He said opponents of the Bill underestimated the terrorist threat, and he rejected comparisons between al-Qaida terrorists and the IRA, which waged a bombing campaign in Britain throughout much of the 1970s, 1980s and early 1990s.

"I've heard opposing politicians say: 'We didn't need these new measures to fight the IRA when they were bombing our cities.' ...

"The difference is that no (IRA member) ever strapped a bomb to their body, walked into somewhere like Trafalgar Square and blew themselves and 100 innocent passers-by to smithereens," he wrote.

He added that large numbers of British "undercover agents, moles and special deep-cover surveillance teams risk their lives daily to track and monitor the evil in our midst. So far, they've managed to frustrate Bin Laden's followers and many are awaiting trial as a result."