ID cards would be of "limited value" against terror and would not have prevented the London attacks in July, says the reviewer of anti-terror laws.
Home Secretary Charles Clarke backs the plan
Liberal Democrat peer Lord Carlile said he had changed his mind on identity cards, which he had previously backed.
"I can't think of many terrorist incidents, in fact I can think of very few... that ID cards would have brought to an earlier end," he told GMTV.
The bill introducing the ID cards plan is currently going through Parliament.
It recently suffered two defeats in the Lords, with peers wanting an entirely voluntary scheme, and ministers wanting people applying for new passports and driving licences to be obliged to go on the ID card register.
"ID cards could be of some value in the fight against terrorism but they are probably of quite limited value," Lord Carlile told GMTV's Sunday programme.
Civil liberties fear
"They would be an advantage but that advantage has to be judged against the disadvantages which Parliament may see in ID cards.
"I certainly don't think the absence of ID cards could possibly have any connection with the events of last July.
"There may be a gain from the security viewpoint in the curtailment of civil liberties, but Parliament has to be the judge about whether the proportion is right."
He added: "I think Parliament is so unenthusiastic about the ID cards that, in reality, this is a debate rather than a reality.
"I don't think they will get through a compulsory ID card system immediately."
Lord Carlile also said he thought the Terror Bill, debated by the Lords this month, had been "rushed".
"I don't think there was a need to rush through the current terror legislation. I would have preferred it to go to a scrutiny committee.
"I think it's led to certain issues being muddled by political debate rather than analysis."
Ministers say ID cards are needed to fight identity fraud and illegal immigration.
The plans were narrowly backed by the Commons last year but the House of Lords tabled a number of amendments aimed at making sure people have a choice.
Conservative leader David Cameron has called ID cards a "monument to the failure of big government".
His comments followed a report which estimated they would cost £14.5bn - which the government denies.
The government is likely to try to overturn the Lords defeats when the ID cards bill returns to the Commons.