David Cameron has vowed to reject a cut in Britain's rebate from Brussels as he prepared to enter talks over the size of the European Union budget.
The Prime Minister said he would be "fighting incredibly hard" for the UK when he joins fellow EU leaders in Brussels for tortuous negotiations over EU spending between 2014 and 2020.
He is calling for a real-terms freeze in the budget but faces fierce resistance from many other member states who, because they are net beneficiaries from the EU, would prefer to accept the significant increase proposed by the European Commission (EC).
The prospect of a cut in the UK's rebate has been raised by both the EC and in revised budget proposals put forward by European Council president Herman van Rompuy.
But Mr Cameron ruled out any further reduction in the rebate beyond what Tony Blair agreed to in 2005.
"The rebate negotiated by Margaret Thatcher is an incredibly important part of Britain's position in Europe and making sure we get a fair deal," he said at Prime Minister's Questions.
"It is absolutely extraordinary that the last government gave away almost half of that rebate and we've never heard one word of apology, one word of regret, for the fact that however hard we fight in Europe - and I will be fighting incredibly hard this week for a good deal - they cut away our feet by giving away half the rebate."
The rebate effectively compensates the UK for the fact that it receives relatively little support under the Common Agricultural Policy (CAP), compared with similarly sized economies like France.
It is currently worth about 3.6 billion euros (£2.9 billion), and meant that Britain's net contribution in 2010 was 7.3 billion euros (£5.9 billion) rather than 10.9 billion (£8.8 billion).
However, it has also emerged that even if Mr Cameron gets the EU to agree a cut in the budget then Britain's payments to Brussels could still end up rising due to the complicated way that contributions are calculated.