Brussels - The European Union's top budget official defended Monday a request for Britain to pay an extra €2bn ($2.5bn) to the bloc, expressing surprise at London's sudden outrage over the matter.
British Prime Minister David Cameron last week vowed not to pay the additional funds into the EU's budget by the beginning of December, taking issue with the size of the bill and demanding emergency talks by finance ministers on the matter.
But EU Budget Commissioner Jacek Dominik said the budget top-up is part of a regular exercise under which member states' contributions are adjusted yearly based on their gross national incomes (GNI). In Britain's case, the GNI was much higher than expected.
"It came to us a little bit as a surprise that ... a typical process, an annual process, repeated for so many years, creates suddenly such a problem," Dominik said in Brussels.
"Up to this moment, there was no single signal from the UK administration that they have a problem with this figure," he added, noting that the budget top-up data had been transmitted to member states on October 17.
In Britain's case, the top-up is based on statistical adjustments covering more than a decade.
Dominik acknowledged the large size of the contribution change for London, but said EU rules specifically state that the difference has to be paid by the first working day of December and do not foresee delayed payments.
He also underlined that if Britain were to seek a revision of those rules, it could also affect one of its most cherished achievements - a long-standing rebate on contributions to the EU budget that most other countries do not enjoy.
The same GNI data that led to the top-up will also pave the way for Britain to get more of a rebate, Dominik warned.
"I think that would be extremely difficult to explain to other member states, why on Monday you like this data (and) on Tuesday you don't," he noted. "If you open this act for future negotiations, you open a Pandora's Box."
The EU rules foresee penalty interest rates if a member state does not make its top-up payment by the beginning of December.
It was not immediately clear when EU finance ministers would discuss the issue, as requested by Cameron. Their next meeting is currently scheduled for November 7.
The British premier has been under pressure from anti-EU politicians, who have been gaining ground in recent elections. A crucial by-election will be held on November 20 in the Rochester and Strood constituency, which the eurosceptic UK Independence Party could win.