It would be a "very great error" for Gordon Brown to break the cross-party consensus on anti-terror laws, shadow home secretary David Davis has said.
David Davis said open cross-party discussions were necessary
Mr Davis said Tony Blair now realises it was a mistake to break the post-July 7 consensus by pushing for suspects to be held for 90 days without charge.
Mr Blair was defeated on that, but the compromise 28-day limit is to be looked at again after Mr Brown becomes PM.
It is among measures ministers say they want to reach cross-party consensus on.
Home Secretary John Reid published a discussion paper on Thursday outlining the measures which he hoped could be agreed on by all parties and form the basis of a new anti-terror bill later in the year.
As well as a possible extension of the 28-day detention limit, it also suggests allowing terrorist suspects to be questioned after being charged, and creating a sex offender-style terrorist register, and a review into courts using intercept evidence.
Mr Reid said he, Prime Minister Tony Blair and the next prime minister Gordon Brown all believed that 28-day detention in terrorist cases was not enough given that suspects had "unconstrained intent... to murder people in their thousands, or potentially, millions".
Detention without charge beyond 28 days
Questioning after charge
Allowing intercept information in court
Register of convicted terrorists
Entry and search powers for police to enforce control orders
Increased security at key gas sites
Set out in law data sharing powers for intelligence and security agencies
Seizure of terrorist's assets (currently only seized if a person is convicted of terrorist finance offence)
"One way might be to legislate now to extend the current limit but to make it clear that there would be extra further judicial and Parliamentary oversight if such measures were ever implemented," Mr Reid said.
Mr Davis, asked about the idea on BBC One's Sunday AM, said 28 days was already double what most "countries like ours" have, including the US which has 10 day limit.
He said judges already regularly reviewed the grounds for any terror suspect being detained without charge up to 28 days, and said it was "unmitigated nonsense" to suggest Parliament could review individual cases.
However, he said if there was evidence to prove a further extension was necessary to protect the public and national security, he would back it.
Until that evidence was presented he would "stand up for the principle" and the long-standing British right of not being locked up without trial.
He said what was important was that Mr Brown and whoever he chooses as his home secretary discuss anti-terror ideas "openly and sensibly" with opposition parties "in private sometimes" and present the evidence so cross-party agreement could be reached.
Consensus was important to avoid terrorists having the advantage of seeing a split establishment, he said.
"It would be a very great error for Mr Brown to break" potential consensus as Mr Blair had done by pushing forward the 90 day detention idea in 2005, he added.