The most fundamental civil liberty is the right to life and preserving that and sustaining that must come before others

Jack Straw

Mr Straw also repeated warnings that prime terrorist suspect Osama Bin Laden and his followers - whom he compared to the Nazis - could be planning further outrages.

"We don't know exactly where. On the one hand, none of us wish to raise anxiety in the minds of the public, but we would be complacent and irresponsible not to warn of the risks," he told BBC Radio 4's Today programme on Friday.

It was Mr Straw's successor as home secretary, David Blunkett, who disclosed that some of those responsible for the attacks on New York and Washington could have previously been in the UK.

Hijackers in Britain

There is conflicting media speculation about the length of their stay and whether any associates are still on the loose in Britain. But Mr Straw reacted forcibly when challenged by Today over why the 11 had gone undetected.

He said he had tried, through the recent Regulation of Investigatory Powers Act, to allow the security services to de-encrypt commercially encrypted (scrambled) e-mails.

It wasn't Big Brother government, it was government trying to put in place increased powers so that we could preserve our democracy against this new kind of threat

Jack Straw

"What happened? Large parts of the industry, backed by some people who I think will now recognise they were very naive in retrospect, said: 'You mustn't do that'.

"The pressure was so great that we and the United States... had to back down a bit.

"Now, I hear people saying 'why were these terrorists here' - well, the answer is not because of any lapse by the intelligence or security services or the police, but because people have had a two-dimensional view of civil liberties.

"The most fundamental civil liberty is the right to life and preserving that and sustaining that must come before others."

However, despite his predecessor's comments, Mr Blunkett later told BBC Radio 4's World at One that "even with the best legislation and will in the world you can't apprehend everyone who passes through an international airport on their way to somewhere else".

Terrorist threat

Asked if the hijackers would have been picked up had stronger powers to read e-mails or monitor phone calls been in place, Mr Blunkett replied that it would unlikely if they were just passing through a UK airport, but that a combination of new measures might be able to track it.

The home secretary also took the opportunity to reassure the public that Britain did not "imminently" face a terrorist attack despite the global threat.

"We are putting in place the necessary security at every point, whether that's for particular facilities, whether it's securing ourselves against internal or external attack."

David Blunkett: Every precaution being taken

Groups that opposed Mr Straw's Regulation of Investigatory Powers Act also sounded a note of caution following his critical comments.

John Wadham, director of civil liberties group Liberty, warned that any curtailing of freedoms "for no good reason" would be a victory for those behind the 11 September attacks.

Liberal Democrat home affairs spokesman Simon Hughes said "If the government think that a law only just on the statute book needs changing literally a few months later, then they must come back with the argument and evidence."

The Confederation of British Industry said a balance between fighting terrorism and the right to privacy for commercially sensitive information had to be found.

Meanwhile the Lord Chief Justice, Lord Woolf, has warned any new anti-terror measures must take the Human Rights Act into account.

"We are a country governed by the law and we mustn't allow the stresses and tensions, which are understandable, to deflect us from that," he told BBC Radio 4's Law in Action programme.