David Cameron was given a bloody nose on Tuesday evening when 91 Tory MPs voted against coalition plans to reform the House of Lords, in the biggest rebellion against the prime minister since he took office.
The government won the vote 462 to 124, a majority of 388, as the Labour Party decided to vote in favour of the Bill to ensure its survival.
However the size of the rebellion by Tory MPs is a damaging blow to Cameron who has faced increasing unrest from those of his backbenchers who are unhappy sharing power with the Liberal Democrats.
And there were reports of an angry confrontation between the prime minister and leading rebel Tory MP Jessie Norman.
Labour MP Karl Turner wrote on Twitter following the vote: "Just witnessed a very angry PM lambasting Tory MP Jesse Norman. Finger pointing and prodding towards Mr Norman."
Turner said Cameron "made bee line for him pointing in his face" and accused Norman of being "not honourable".
According to reports Norman was later advised to leave the building by Conservative Party enforcers, the whips, for his own good.
The row over House of Lords reform claimed its first government scalp early on Tuesday evening when Conor Burns resigned as a junior member of the coalition.
Burns, a ministerial aide to Northern Ireland secretary Owen Paterson, told MPs that he could not support the Bill at second reading.
The MP for Bournemouth West is one of two junior members of the government who had indicated that they cannot support Nick Clegg's plans to turn the Lords into a largely elected chamber.
Angie Bray, who is parliamentary private secretary to the Cabinet Office minister Francis Maude, also confirmed to The Huffington Post that she would vote against second reading.
However she added that she would not resign and would force David Cameron to sack her, which he promptly did following the vote.
Earlier on Tuesday the government admitted it could no longer dictate the timetable of the Lords Reform Bill and abandoned a programme motion vote scheduled for later on Tuesday night.
It was an acknowledgement that it faced a massive rebellion from Tory MPs who opposed major constitutional changes being given only 10 days of debate on the floor of the Commons.
Leader of the House of Commons Sir George Young has confirmed the government has ditched the "programme motion" which would have set the number of days MPs would spend discussing Nick Clegg's plan to introduce a largely-elected House of Lords.
The U-turn means the Bill on Lords reform is now in limbo until at least September, and the onus is on David Cameron to try to win rebel Tories around over the summer.
The Bill will now proceed to a committee of the whole House, where it is likely to still face filibustering from Tories who oppose in principle the vision for an elected House of Lords.
Lib Dem deputy leader Simon Hughes said it was up to Cameron to find a way to take the legislation forward - and he warned there would be "consequences" for the coalition if he failed to do so.
"The prime minister clearly has to work out how he can deliver his side of the coalition bargain," Mr Hughes told the BBC Radio 4 Today programme.
"We have delivered every element of the coalition agreement. We have delivered our people through the voting lobbies in every case. A deal is a deal.
Hughes made it clear Lib Dems would consider blocking planned changes to the electoral map, which could be crucial in helping the Tories win the next election, if the prime minister was unable to deliver Tory votes on Lords reform.
"The one thing that is obvious that the Tories desperately want is the boundary commission proposals to go through which is an advantage to them," he said.