Civil liberties must not be undermined by the government as it responds to the London bomb attacks, prime minister Tony Blair's wife Cherie has warned.
Cherie's comments come as ministers plan further measures
It would be "all too easy" to fight back in a way "which cheapens our right to call ourselves a civilised nation", said the barrister in Malaysia.
She stressed her comments should not be seen as making light of the attacks.
But Tory homeland security spokesman Patrick Mercer said the remarks came at a "desperately insensitive time".
Cherie, a QC who practises under her maiden name Booth, said: "Nothing I say here could possibly be construed as making light of those horrible acts of violence, or of the responsibility imposed on the UK and other governments to keep the public safe, or of the difficult and dangerous task performed by the police and intelligence services."
But, she added "at the same time it is all too easy for us to respond to such terror in a way which undermines commitment to our most deeply held values and convictions and which cheapens our right to call ourselves a civilised nation".
The QC, addressing an audience of 1,000 lawyers, civil servants and diplomats in Malaysia, said judges made rulings in a way that taught citizens and government about the "ethical responsibilities" of participating in a true democracy committed to "universal human rights standards".
She said courts should be "guardians of the weakest, poorest and most marginalised members of society against the hurly-burly of majoritarian politics".
A good example of this working was the decision by the UK's highest court, the House of Lords law lords, that the UK's policy of holding foreign terrorist suspects indefinitely without charge broke human rights laws.
"What the case makes clear is that the government, even in times when there is a threat to national security, must act strictly in accordance with the law," she said.
But Mr Mercer said: "Cherie Blair or Cherie Booth, whichever name she's going under just at the moment, is entitled to her private opinions of course and to express those.
"But she is the prime minister's wife and I think this is a desperately insensitive time for her to be making those sorts of comments."
Mr Blair says tackling the ideology behind the attacks is key
Mr Blair says extra powers being looked at include extending the time people can be held without charge.
On Tuesday Mr Blair vowed not to "give an inch to terrorism" and said Iraq was no excuse for the London bombings.
He said 11 September 2001 was a wake up call for the international community, but argued some people "then turned over and went back to sleep again".
"Let us expose the obscenity of these people saying it is concern for Iraq that drives them to terrorism. If it is concern for Iraq then why are they driving a car bomb into the middle of a group of children and killing them?
"We are not going to deal with this problem, with the roots as deep as they are, until we confront these people at every single level - and not just their methods but their ideas," he added.
Also on Tuesday Mr Blair held talks with Conservative leader Michael Howard and the Liberal Democrats' Charles Kennedy about possible new powers to tackle terrorism.
These could include allowing the use of "phone tap" evidence in court.
Mr Howard said the Tories saw difficulties with calls from the police to extend the time a terrorist suspect can be held without charge from 14 days to three months.
Police chiefs say they only want to be able to ask a judge to extend detentions bit-by-bit up to the new time limit.
Mr Kennedy said "reasonable progress" had been made in the talks and he hoped this would continue in a measured way so "we don't surrender basic civil liberties in the process".
There is already agreement on proposals to create new offences of engaging in acts preparatory to terrorism and of indirect incitement to terrorism.