David Cameron, pictured with other EU leaders on Friday, says the UK will not pay the bill by 1 December
Europe expects the UK to pay an extra £1.7bn towards the EU budget "and that's that", a vice president of the European Parliament has said.
Alexander Graf Lambsdorff, a German MEP, said the EU would be "exasperated" if the UK tried to avoid payment.
On Friday David Cameron said the EU had "another think coming" if it thought Britain would pay the bill by the 1 December deadline.
The EU demanded the extra amount because of growth in the UK economy.
Mr Lambsdorff told the Today programme on BBC Radio 4 that "everybody has to pay their dues".
He added: "If you have higher GDP growth than forecast, that also means logically that you have a higher contribution to the community's budget.
"That is a logical consequence. That is something that everybody has signed up for."
But Conservative MP Sir Bill Cash, speaking on the same programme, said it was "quite common" for member states to ignore EU demands.
"There may be consequences, but then they have to be weighed up," he said.
Sir Bill - who chairs the European Scrutiny Committee in the Commons - also said he would call in treasury ministers to his committee to see "how they intend to handle it from now on".
Negotiation and compromise
UKIP's deputy leader, Paul Nuttall, said Mr Lambsdorff was "absolutely right" and that Britain would have "no choice" but to pay.
"It would be illegal not to pay up," said Mr Nuttall.
"But this is what we have signed up to. Frankly I think we would be better off outside this organisation, where the British taxpayer wouldn't be forced to hand over £1.7bn by 1 December.
"Mr Cameron can turn around and say he won't pay by the deadline. But he hasn't ruled out paying at all - because he will have to."
Former foreign secretary Sir Malcolm Rifkind said it was "ridiculous" to expect Britain to pay by 1 December.
But he said he expected a "political negotiation and a sensible compromise".
David Cameron said the bill was "completely unacceptable"
Meanwhile, Labour has asked why the Treasury was notified of the bill days before Mr Cameron. They also questioned why the government failed to realise there was a potential issue earlier in the process.
In a letter to George Osborne, shadow chief secretary to the Treasury Chris Leslie said the chancellor has "serious questions to answer about how long the UK Government has known about the possibility of a higher surcharge for the UK."
He added: "The Office for National Statistics published a report over four months ago detailing the changes made to UK growth figures which it stated were for use in the calculation of a Member State's contribution to the EU Budget."
On Friday the European Commission President Jose Manuel Barroso said the demand was made under a system agreed by all the member states.
EU finance ministers have agreed to the UK's request for emergency talks about the top-up payment, which would add about a fifth to the UK's net EU contribution of £8.6bn for this year.
The prime minister said on Friday he was "downright angry" and that the British public would find the "vast" sum "totally unacceptable".
He said: "It is an unacceptable way for this organisation to work - to suddenly present a bill like this for such a vast sum of money with so little time to pay it.
"It is an unacceptable way to treat a country which is one of the biggest contributors to the EU."