"If I may use the phrase, this is a club - and Britain has a great tradition of clubs. And you cannot go to a beef-eaters' club and say you are a vegetarian. You have no influence," pointed out the commission president.

He added that "until now Mr Brown has not been one of the EU's big players - even at finance minister level - because of Britain's refusal to join the euro," the Telegraph reported.

Gordon Brown is described by British press as one of the most eurosceptic ministers in the Labour government.

He has resisted calls for introducing the euro in the UK, arguing that the British economy is not ready as measured by "Brown's five economic tests," including euro entry impact on jobs and investment in the UK.

He also reportedly influenced Tony Blair's resistance to the EU budget agreement last June which threatened to provoke a crisis among the bloc's leaders, already disappointed by the failure of the EU constitution in French and Dutch popular polls.

Following the December budgetary deal under the UK presidency, Mr Brown has recently re-opened the issue on the grounds of different views on how the so called "British rebate" from the EU budget should be calculated.

He is a stern supporter of European economic reform and has rankled EU colleagues by his preachy style. But in a major speech last month, Mr Brown himself argued the UK should redefine its role in Europe.

"Some present the issue of Europe as in or out, empty chair or total subjugation. I see it differently," he said, according to BBC.

Even if the UK stays out of the euro, it should strive "to complete the single market in utilities, energy, telecommunications and services generally and in particular financial services," he added.

He also said London should stop lamenting the lack of reform on the continent and instead work more closely with European partners, leading the way on change.

According to the Telegraph, Mr Barroso's comments on Mr Brown were received in a "relaxed" way in the UK treasury, while some insiders defended their boss by pointing out that he had been the "leading voice" in recent EU financial decisions such as tax harmonisation moves.