David Cameron has received a major boost from Barack Obama after the US president firmly backed his EU negotiations in their White House press conference.
Obama's comments will not calm the atmosphere in a febrile Westminster, as turmoil and infighting among Conservative backbenchers and Cabinet ministers intensifies in London ahead of Wednesday's key vote.
But they will strengthen Cameron's hand by playing down fears that the uncertainty created by the possibility of an in-out referendum in could destabilise the 'special relationship' between Britain and the US.
"David's basic point that you probably want to see if you can fix what's broken in a very important relationship before you break it off makes some sense to me," Obama declared.
"I know David's been very active in seeking some reforms internal to the EU.
"Those are tough negotiations, you gets a lot of countries involved, but so long as we haven't yet evaluated how successful those reforms will be I at least would be interested in seeing whether or not those are successful before rendering a final judgement."
Many of those backing eurosceptic John Baron's amendment to the Queen's Speech regretting the lack of an EU referendum bill believe the UK will not be able to secure any agreement from European leaders on a fresh set of terms for British membership - making Cameron's strategy of attempting to seek agreement unrealistic.
Education secretary Michael Gove and defence secretary Philip Hammond generated headlines of their own yesterday by revealing they would vote to leave the European Union if a referendum were held now.
Other senior Tories, including former chancellor Nigel Lawson and former defence secretary Michael Portillo, have been outspoken in their criticism of Cameron's renegotiation plans.
The prime minister confined his remarks in the White House press conference on the issue to general commitments to pursuing "Britain's national interest", but had earlier fired a broadside at malcontents within his party.
"The point I would make to these people is to give up before a negotiation has started seems to me an extraordinary way to go about things," he said.
"The idea of throwing in the towel before the negotiations have even started is a very strange opinion."
Cameron also defended his strategy of allowing backbench MPs to vote for the EU amendment while asking ministers to stay away from the vote. The prime minister's spokesperson said ministers had been told that "if they so wish they can abstain".
Cameron said: "It is a very sensible approach. Coalition does throw up different circumstances.
"I think it is a very sensible approach to say it wouldn't be right for ministers to vote for an amendment to their own Queen's Speech, so it makes sense for ministers to abstain.
"But equally it is perfectly acceptable for Conservative MPs to vote for this amendment, which is in line with the party's policy.
"I think reading some of the headlines over the weekend I think people are getting slightly overexcited."
Baron rejected the argument that the Conservatives may struggle to get a referendum bill through parliament as "weak" and insisted "there was no downside in trying".
"Whether successful or not, all MPs would need to declare their hand – and the electorate would take note," he pressed.
The war of words came as John Major's former press secretary, Sheila Gunn, said the EU debate was increasingly resembling the fights which tore the party apart in the early 90s.
"One of the differences is that was when the Conservatives had been in power for 17 or 18 years. Now the Conservatives have only been in power in coalition for two or three years," she told the Huffington Post.
"I would really expect the Conservative MPs to show some common sense. I understand they have strong feelings on the matter, but is now really the right time to make a fuss of it?"
She added: "You could also say now that the Conservative party is handing the election to the Labour party."
Former foreign secretary Sir Malcolm Rifkind told the Today programme prime minister the prime minister was being put in an "impossible situation" by eurosceptics agitating for the division.
"Sometimes it's sadly necessary to split your party on a great issue of principle. But to split your party on an issue of tactics seems to me pretty odd," he said this morning.
"What they're doing is putting the prime minister in an impossible situation. He cannot simply vote for this amendment because it would split the coalition right down the middle, but at the same time the motion cannot win because there is not a parliamentary majority for it.
"All those supporting it will achieve is split their own party, cast questions over the prime minister's authority and indirectly help Labour's prospects at the next general election."
Downing Street tried to cast a more positive light on the situation by bizarrely claiming the furore was to be welcomed in No 10 because it helped publicise Cameron's January Europe speech.
"The prime minister's view is that it is no bad thing for a spotlight to be shone on his commitment that should he remain the prime minister [after the 2015 general election] he will have an in-out referendum and that will happen following a period of renegotiation," the prime minister's spokesperson added.
The comments by former Conservative Cabinet minister Lord Forsyth on BBC2's The Daily Politics programme suggested this was not all positive for the prime minister, howeer.
"I think David Cameron’s thinking he can persuade the golf club to play tennis and I think his negotiating position is impossible because he's saying 'and if I don't succeed I'll continue to play golf'," he said.
"He's said that in the event of not being successful in the negotiation that he would still campaign to remain in the EU."
Cameron pointed out the benefits of the EU's trade negotiating power in a comment piece for the Wall Street Journal newspaper this morning, arguing the free trade deal with the US could make all involved better off.
"Trade makes the cake bigger so everyone can benefit," he wrote. "This deal could add as much as £10 billion to the British economy."
Downing Street has suggested the free trade deal could have a major impact on the UK, making each family £380 a year better off each year.
London mayor Boris Johnson managed to both support and undermine his party leader in a single sentence in his weekly column for the Telegraph newspaper.
"He has my full support, and I personally back legislation now to make sure that referendum goes ahead," Johnson declared.
"It will be a good thing for everyone, because we will all have to focus not on the feud – so toxic, so delicious, so gloriously fratricidal – but on what is actually right for the country; on the nuts and bolts of what we are trying to achieve."
Cameron is not the only party with a Europe headache to deal with this week, either. A group of Labour MPs including Keith Vaz has called on Ed Miliband to back a referendum deal now.