As Eurosceptics at home leapt on news that the EU executive -- branded a "thirsty vampire" -- had demanded a sum worth about one seventh of London's annual payment after a major statistical review of national incomes, Cameron demanded action from fellow leaders at a summit calling the bill "completely unacceptable".
He found some sympathy - a visibly furious Cameron told a news conference that Italian Prime Minister Matteo Renzi had also lambasted "bureaucrats without a heart", who made it harder to persuade citizens of the Union's value.
"It's an appalling way to behave," Cameron said. "I'm not paying that bill on Dec 1. If people think I am they've got another thing coming. It is not going to happen."
EU ministers will hold an emergency meeting on the issue next month.
Cameron said he wanted to understand the technical calculations and was also ready to mount a legal challenge.
EU officials insisted the revision, which also saw Italy and even crisis-hit Greece asked to pay more while France and Germany would get rebates, was part of an annual statistical exercise handled by civil servants, not politicians.
Jose Manuel Barroso, outgoing president of the European Commission, defended his staff, telling a news conference the system was designed by national governments which provided the income data on which payments were calculated.
He said the EU executive would explain the calculation to ministers but there could be no question of changing what countries had determined were their gross national incomes.
Cameron noted that annual revisions to the payments had never been so great - an effect, EU officials said, of a once-in-a-generation review of how national incomes are calculated that found Britain was richer than it had previously declared.
Officials at EU statistics office Eurostat said that was a result mainly of taking more account of money flowing in 2002-09 to non-profit organisations - from churches and universities to trade unions, charities and sports clubs.
Those statistics are provided by national agencies and, a spokesman for the European Commission's budget directorate said, the revised calculations, which then have an impact on working out the annual contribution to the EU budget, had been reviewed by officials from national governments, as happens every autumn.
"This is a purely mathematical, technical process," he said. "So much so that member states agreed that the Commission can implement the adjusted figures by Dec 1 every year without any need to submit a proposal to the Council (of EU leaders)."
However, governments have little awareness of how other states may be amending their income calculations until the data is put together by Eurostat in the final weeks, leaving the size of any budget adjustment open to potential surprises.
The apparent lack of awareness of the political sensitivity of such big adjustments this year overshadowed a day of summitry intended to review efforts to revive economic growth.
The leaders also came up with 1 billion euros ($1.3 billion) of cash commitments to fight the Ebola outbreak in West Africa.
After an EU deal to curb climate change overnight, the anger on Friday at Brussels' officials may dampen the final week of the present Commission led by Jose Manuel Barroso.
He will make way for incoming President Jean-Claude Juncker on Nov 1 after 10 years in charge of the European Union's executive branch.
Juncker has pledged a "very political" rather than technocratic approach to try to regain the trust of the half-billion people in the EU, many of whom are turning to anti-EU parties like the UK Independence Party.