European leaders have agreed to David Cameron's demand for emergency talks after the European Commission made a shock call for Britain to pay an extra £1.7bn to Brussels.
The surprise bill from EU officials could not have come at a worse time for the prime minister, as the Conservatives battle to prevent Ukip winning the Rochester by-election next month.
Cameron is coming under pressure from his own MPs to refuse to pay the cash - which is due by December 1. It has been reported that the prime minister broke into a general discussion of the European economy today to demand that leaders of the 28 member-states address the proposed surcharge.
It is understood that British officials did not learn about the demand until last week. The surcharge - which would add almost a fifth to the UK's annual contribution of £8.6bn - is intended to reflect Britain's better-than-expected economic performance relative to other EU states.
His intervention sparked an hour-long debate, in which several other leaders facing surcharges spoke up, including Italy's Matteo Renzi.
The leaders of European Union member states, including Cameron, were pictured in what look like tense exchanges with the leaders of the Commission in Brussels today.
Commission President Jose Manuel Barroso speaks with the Italian Prime Minister Cameron
Preliminary figures seen by the Financial Times suggest that Britain is facing by far the biggest top-up, while the Netherlands is being asked for an extra 642 million euro (£506 million).
By contrast, Germany receives a rebate of 779 million euro (£614 million), France one billion (£788.7 million) and Poland 316 million (£249 million).
Cameron last night discussed how the demands could be challenged with Dutch counterpart Mark Rutte, who said his government was looking into the legality of the demand for more cash, which came as "an unpleasant surprise (which) raises an awful lot of questions".
Barroso, right, speaks with Italian Prime Minister Matteo Renzi
Ukip leader Nigel Farage said the "outrageous" demand created "real political trouble" for the prime minister. "The EU is like a thirsty vampire feasting on UK taxpayers' blood. We need to protect the innocent victims, who are us," said Farage. "He's in a very weak position. He can do nothing about this.
"And I think, really, he's now being pushed into a position where, unless he brings forward his referendum promise, I think he's in real political trouble."
The EU demand is a huge boost for Ukip ahead of the Rochester by-election, triggered after Mark Reckless defected from the Tories. The Conservatives are worried that a Reckless victory would cause panic on the Tory benches and potentially lead to more defections.
Cameron and President of the European Council Herman van Rompuy
Conservative MP Mark Pritchard said: "The timing and content of the EU budget demand shows how inept Brussels is. Brussels needs to work with the UK Government, not work against it.
"Unless this behaviour changes, the EU referendum could be brought forward. Europe should not penalise the UK's economic success whilst rewarding France's economic failure."
Commission spokesman Patrizio Fiorilli said the figures were produced by a "mechanical" calculation and the demand was "not politically motivated".
"Britain's contribution reflects an increase in wealth, just as in Britain you pay more to the Inland Revenue if your earnings go up," he said.
The demand for money has also been criticised by Labour and the Lib Dems. Shadow Europe minister Pat McFadden said: "It's unacceptable that the outgoing EU Commission should spring a backdated bill on member states in this way. But UK ministers have known about this since last week.
"The Government should be pushing for the best deal possible for the UK. The Prime Minister must now make up for lost time, and should be working in step with other affected member states, including the Netherlands and Italy.
"This is a proposal made by the outgoing EU Commission, and with a new Commission taking office imminently. So it is imperative that David Cameron now urgently discuss this with other member states, and urges the incoming EU Commission to look again at the proposed change.
"Labour argued against the proposed increase in EU spending in 2012, and voted for a real-terms cut in the EU budget then. We have argued for reform of the EU budget, including a greater focus on generating growth and jobs, and for the EU to undertake a zero-based review of all spending by EU agencies."
A Liberal Democrat spokesman said: "The Liberal Democrats do not think it is acceptable to change the fees at the drop of a hat and demand Britain cough up £1.7 billion. We will work with other parties and countries that have just been landed with similar bills to challenge this."
"It is not acceptable to have a demand such as this seemingly presented as a technical adjustment. It requires detailepolitical discussion," the spokesman said.