The EU referendum bill could well be killed off in the Lords, after over 70 peers signed up to speak in the debate.
There will be no vote on James Wharton's government-backed private member’s bill today, but the number of people signing up to speak could kill off the bill with multiple amendments - probably those proposed by the Lords constitutional committee.
A barrage of amendments could keep the debate going beyond February 28th, the date by which it needs to return to the Commons if there was to be time for it to pass.
That would be an ideal situation for Labour, which opposes the bill but does not want to be seen to be voting against it for fear of a public backlash.
"The British people . . . will not forgive Labour and the Liberal Democrats if they try and scupper this bill because they don’t trust the British people," Wharton said.
“It is extremely important that the House of Lords recognise that this bill, which has been passed through every stage of the democratically-elected House of Commons, needs to pass in order to give the British people a say on this very important issue.
"It would be strange indeed for the unelected House of Lords to block a Bill which is to legislate for a referendum."
The Tories would hit out against Labour and the Liberal Democrats if the bill was held up, but the main victim of any such move would be David Cameron, who would come under severe pressure from eurosceptics in his party to bring forward a government bill.
Any such attempt would be instantly shot down by the Lib Dems.
"Are we to add to the despair that exists about the political system?" former Thatcher minister Lord Crickhowell said.
"Are we going to block the wishes of ordinary people who want certainty that their views will be heard?"
Lord Dobbs, who is piloting the bill through the Lords, said the debate over the EU had become poisonous.
"It's become a pestilence; it's become a poison in our political system; it dominates so much of our political dialogue here and we need to get rid of this burden", he told the Today programme.
Pro-European peer Lord Mandleson said: "I think by in effect threatening the rest of Europe with our exit if we don’t get exactly what we want will diminish, not enhance, our ability to get much needed reform in Europe.
"I just don’t think in Brussels or Berlin or Paris you're going to gain an audience and the support you need by holding a pistol to Europe's head and saying 'agree with us on everything we want or we're leaving'. I don't think that's the right way to win the central argument for reform."
Any failure in the bill would significantly bolster Ukip's election prospects. Cameron managed to cut down its support from 20% to closer to ten per cent following his commitment to an in-out referendum in 2017.
The debate comes as European Commission vice president Viviane Reding accused Cameron of lying about the EU and immigration.
"This supposed invasion of foreigners coming to the UK and stealing the jobs and stealing the social security and the health money. The fact and figures, and we all know this, show it is simply not true," she said.
"What is leadership if you just try with populistic movements and populistic speech to gain votes? You are destroying the future of your people," she said.
"That is what I'm really worried about. That is why I ask help from all the reasonable forces in Great Britain in order calmly to explain what are what Europe is about and what Europe can do and what Europe can't do, what Europe does and what Europe does not do because most of the things which are told to the people in Great Britain are myths, have nothing to do with reality."
Lord Dodds is staying in the UK to see the bill through the upper house rather than going to the US to see his House of Cards drama receive a nomination for the Golden Globes.