Britain says its prime minister is protesting a European Union request for an additional 2.1 billion euro ($2.65 billion) contribution to the EU coffers at a time of increasing pressure at home for the country to leave the bloc.

A British official, who asked for anonymity because of the sensitivity of the issue, on Friday confirmed a report in the Financial Times that his nation had been asked to top up its contribution by some 20 percent because of its improving economy. He said the Netherlands had also been asked for a top-up.

The European Commission did not immediately respond to the complaint.

A longtime reluctant member, Britain has seen a surge in the popularity of the UKIP party which wants to get Britain out of the EU.