International terrorism has increased governments' enthusiasm for "repressive measures" that could undermine justice, the UK barristers' leader has warned.
Mr Mansfield said terror laws could undermine justice
Chairman of the Bar Council, Guy Mansfield QC, said terror suspects must not be denied legal and human rights.
Even those charged with "the most appalling crimes" were entitled to basic rights, he said.
His comments come as UK ministers plan a number of new measures to tackle terrorism after the London bombings.
The government has announced plans to hold parts of trials in secret and new deportation laws in the wake of July's attacks.
Mr Mansfield will tell the opening of the Commonwealth Law Conference in London that terror suspects should not be denied their legal rights even if they are accused of the most appalling crimes.
'Freedom under the law'
"Governments are moving to address internal dangers with greater enthusiasm for repressive measures," he will tell the audience of lawyers and judges.
"Whatever is the right strategy in the fight against terrorism, even defendants charged with the most appalling crimes remain entitled to basic rights.
"We believe in freedom under the law without exceptions. Those tenets face real challenges today.
"We must be careful our governments do not create a new category of defendant denied basic rights hitherto thought indispensable."
Under proposals set out by the government, defendants may not be allowed to see some of the evidence against them, with "special advocates", who have been security vetted by MI5, representing them in court instead.
In August, Home Secretary Charles Clarke also announced new deportation rules for people who foment, justify or glorify terrorist violence.
Earlier this month Prime Minister Tony Blair vowed not to soften his crackdown on terrorism at home or abroad.
Speaking during a visit to India, Mr Blair said: "We are not stopping any freedom of speech. But with freedom comes responsibility and you have to draw a line.
"You have to make a judgement in the end about what is right and what is wrong. We have to take that clear line and we have to see it through.
"I set the process out very deliberately. We are going to take these measures. They will be tested in the courts and let us see what happens."