Pro-Government peers are planning to rewrite the Terrorism Bill to let police hold suspects without charge for up to 60 days.
They claim that the 28-day limit set by MPs is too short, but critics say they are engaged in political manoeuvring.
Lord Sewel, a life peer and former minister, said yesterday that he would push for a vote when the Terrorism Bill goes through its final stage in the Lords later this month. He is convinced the police will need more than 28 days to question suspects when they are investigating complex international terrorist networks.
Tony Blair suffered the only important Commons defeat of his eight years in office when the House threw out a request from the Metropolitan Police to be allowed to detain suspects for up to 90 days, which the Prime Minister had backed personally. But if the pro-Blair alliance of Labour and independent peers succeed, they will go some way towards undoing the defeat.
Baroness Ramsay of Cartvale, a Labour peer and former intelligence officer, said: "It's our duty, as well as our right, to ask the Commons to think again. They never debated the proposal that there should be a limit of up to 60 days - and it's 'up to 60 days', not '60 days', just as it was 'up to 90 days'. I cannot understand how responsible senior people can look at the evidence and think that's it's not compelling."
Lord Foulkes of Cumnock, a former minister, said: "Sixty days would be not as good, but it would be nearly as good as 90 days. Tactically, we think it has got the best chance of getting through."
However, Shami Chakrabati, the general secretary of the civil rights pressure group Liberty, accused the peers of being motivated by "pique".
"They have just plucked this figure out of the air, just as 90 days was plucked from the air," she said. "This is not about how long people can be held while they are awaiting trial, it's about how long police can hold them without giving the reason why they are locked up.
"This is politicking, because there was a government defeat and some people haven't got over the shock to their system that the belief in the rule of law actually triumphed in this case."
Even the reduced figure of 28 days, set by MPs, has been criticised in an unpublished letter from the UN Commissioner for Human Rights, Louise Arbour.
The letter, written in November and deposited in the House of Commons library by the Home Secretary, Charles Clarke, criticised the Bill for not giving a precise definition of terrorism, and said the clause that bans organisations which "promote or encourage terrorism" could be interpreted to mean that a person is guilty of "disseminating" terrorist literature "even if s/he had no intention of doing so".
Ms Arbour, a former member of Canada's High Court of Justice, warned that "certain provisions of this Bill could pose grave challenges to effective human rights protection and set worrying precedents in the global struggle against terrorism."
However, her remarks were rejected by Mr Clarke. In a written reply, he said: "The High Commissioner has specific concerns about the Bill. We do not believe that these are justified. The Government is satisfied that these clauses constitute a proportionate and necessary response to the threat of terrorism."Reuse content