Tonight's vote over 42-day detention is going to be "very, very close" with the full pressure of the government machine being brought to bear, civil liberties campaigners are saying.
Speaking to politics.co.uk at a protest outside parliament yesterday, Shami Chakrabarti, director of Liberty, said: "It's going to be very, very tight.
"We're still hopeful, but goodness me, the full pressure of the government machine is against us. All we've got is reasoned argument and ancient principles to fight back with."
The comments come as foreign secretary David Miliband had his trip to Israel cut short so he could come back and vote for the plans, showing just how tight the vote has become.
A further mark of government desperation came when minister made further concessions today, with the promise of a compensation deal for suspects held but not charged.
Ms Chakrabarti was joined outside parliament by shadow home secretary David Davies and Liberal Democrat home affairs spokesman Chris Huhne. The protestors released 42 balloons with the words 'charge or release' on them.
politics.co.uk pushed Ms Chakrabarti on what campaigners would do if the vote went against them.
"If it goes wrong then we fight on in the House of Lords," she answered.
"People have different views about the Lords but if it has one purpose it's as a backstop to protect our fundamental rights and freedoms when the hubbub of politics lets us down.
"But I'm really concentrating on the Commons because I've spent many months talking with Labour MPs and I know that on a free vote we would win," she added.
"But politics means that other pressures come to bear."
Asked whether groups like Liberty still had any faith in Gordon Brown after his push for increased detention, Ms Chakrabarti said: "I'm an optimistic person and I have to be in this job.
"This is not a great episode. But if Labour MPs send him a message then maybe his government and his legacy can be saved."