The UK has been told it must pay an extra £1.7bn (2.1bn euros) towards the European Union's budget because of the country's relative economic health.

The additional payment is a result of new calculations by the EU, which determines how much each member state should contribute based on gross national incomes.

The £1.7bn would add almost a fifth to the UK's annual net contribution.

It comes at a time of increased pressure on David Cameron over Europe.

The recent success of the euro-sceptic UK Independence Party in by-elections has prompted renewed calls for the prime minister to renegotiate the terms of the UK's relationship with Europe.

The BBC's political correspondent Ben Wright in Brussels says the demand for more cash has infuriated the government and will rile many backbench Tory MPs.

Mr Cameron is currently meeting other EU leaders for a summit in Brussels.

A government source told the BBC: "It's not acceptable to just change the fees for previous years and demand them back at a moment's notice.

"The European Commission was not expecting this money and does not need this money and we will work with other countries similarly affected to do all we can to challenge this."
'Harms EU relationship'

The additional payment was requested after the European Commission's statistics agency, Eurostat, reviewed the economic performances of member states since 1995, and readjusted the contributions made by each state over the last four years - based on their pace of growth.

Under the new calculations, the UK and the Netherlands are both being asked to pay more, while France and Germany are both set to receive rebates.

The additional payment is due on 1 December.

Mr Cameron is meeting his Dutch counterpart, Mark Rutte, to discuss how they might challenge the surcharges.

Patrizio Fiorilli, a European Commission spokesman, said the additional request for funds "reflects an increase in wealth".

"Just as in Britain you pay more to the Inland Revenue if your earnings go up," he said.

But the leader of the Conservative MEPs, Syed Kamall, said the UK was being penalised for its austerity measures.

"The European Commission is penalising Britain for taking tough decisions, putting in place a long-term economic plan and for having the most successful economy in the EU, while actually rewarding France for being an economic basket case," he said.

"David Cameron is absolutely right to stand up to this attempted daylight robbery by the EU."

"This is outrageous and harms the EU's relationship with Britain. At times like this, the European Commission can be its own worst enemy."