The attorney general says he is not convinced the government should extend the detention of terror suspects without charge beyond 28 days.
Lord Goldsmith says he has not seen evidence to support extension
Lord Goldsmith said he had seen no evidence to support such an extension.
He spoke after Tony Blair said he still backed plans for an extension to 90 days, despite its defeat by MPs.
Tory shadow home secretary David Davis said Lord Goldsmith's comments showed "unequivocally" that the Tories had been right to oppose the 90-day plans.
A Downing Street spokeswoman refused to say anything about Lord Goldsmith's comments.
Lord Goldsmith said: "The recent investigations demonstrate that it was right to extend the period to 28 days, but on extending it any further we need evidence to demonstrate that that is needed."
Last year, the Commons voted down the government's plans to bring in a 90-day limit on detentions, with MPs and peers eventually settling on 28 days. Previously, the limit had been 14 days.
The prime minister has said he remains in favour of a longer detention period, as asked for by police, but wants to proceed by consensus.
And on Sunday, Home Secretary John Reid said he would consider extending the time limit if police presented enough evidence to support it.
Mr Davis told BBC News: "What the attorney general is saying is, what we thought all along, that there's no evidence there to argue for more and that 28 days, as it stands, is sufficient."
Ministers were seeking the extension "for party-political advantage rather than making the public safer", he added.
The BBC's Reeta Chakrabarti said that, if the issue returned to Parliament, the words of the attorney general would make it much more difficult for Mr Blair to change the minds of MPs who were already sceptical.
But Lord Goldsmith did raise the prospect of the questioning of suspects after charge.
He said that, if post-charge interviews were introduced, there would be safeguards to ensure suspects were not "browbeaten time and time again" by police interviewers.
Such interviews would not be restricted to terror suspects, but people suspected of other crimes as well.
"While terrorism is top of the agenda I don't think that it needs to be restricted to that," he said.
Lord Goldsmith also said work was continuing to find a way in which telephone intercept evidence could be used in court without compromising the sources of the material and the methods used.
Earlier, Mr Reid said he had yet to see any evidence to support the introduction of phone-tap evidence in court cases
Lord Carlile, the government appointed expert who oversees terrorism laws, has said he expects new anti-terror measures, possibly including an extension of detention to 90 days, to be published early next year.