'As you read this, there are at least 100 Osama bin Laden trained terrorists walking Britain's streets,' Stevens wrote in an editorial in News of the World published Sunday. The number is probably closer to 200, since the 'cunning of Al Qaeda' makes it difficult to generate an exact number, he said.
'But they would all commit devastating terror attacks against us if they could, even those born and brought up here,' he said.
The article, headlined 'Forget human rights, kick out the fanatics', endorsed the controversial Prevention of Terrorism Bill, now before the House of Lords.
The bill, which seeks to give sweeping rights to the police and security agencies including arrests without charges, has been challenged on the grounds that it violates civil rights.
Rejecting these arguments, Stevens said: 'For the safety of the vast majority, occasionally we will have to accept the infringement of the human rights of high-risk individuals.'
Those opposing the anti-terror laws 'simply haven't understood the true horror of the terrorism' that's facing UK. 'Some of the reports that crossed my desk in the last few months alone made my hair stand on end,' said Stevens, 62, who retired February 1.
'I've heard opposing politicians say: "We didn't need these new measures to fight the IRA when they were bombing our cities", ' but ' 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.
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.'
However, a terror strike is 'inevitable' unless strong anti-terrorist measures are taken immediately, he warned.