A move to increase detention for terror suspects to 60 days without charge has been defeated by peers.
The Terror Bill was put together after the July bombings
The House of Lords voted 210 to 108, a majority of 102, against it during the report stage of the Terrorism Bill.
In November, in Tony Blair's first Commons defeat, MPs decided that 28 days - rather than the current 14, or the proposed 90 - should be the limit.
On Wednesday some peers suggested that 60 days would be a better compromise, but other Lords disagreed.
The group of peers arguing for 60 days was led by Labour backbencher Lord Sewel, and the former head of the Metropolitan Police, crossbencher Lord Imbert.
They said it would enable the police and intelligence services to gather vital evidence to secure a conviction.
Lord Sewel said: "In cases like this there can be no objective right answer - no magic wand to predict a magic number.
"The more I have considered, the more I have read, the more I have heard, the more convinced I am the number is somewhere between 28 days and 90 days."
And opposition spokesman Lord Henley argued against 60 day detentions.
"We believe it is wrong in principle," he said.
"It is equivalent to a six months custodial sentence and tantamount to imprisonment. We have moved from seven days to 14 days to 28 days.
"A further move to 60 or 90 is something much greater and I think one can argue that that is wrong in principle."
The Conservative front bench backed the 28 day decision, and Home Office Minister Baroness Scotland argued that although Labour backbenchers had a free vote on the issue she and the rest of the government front bench were abstaining.
"It is for the Lords to determine what stance it is wise to take in relation to these matters," she said.
The Terrorism Bill was introduced following the London bombings of 7 July last year, in which four suicide bombers killed 52 people.