The president of the European Commission has warned that Britain would become like "Norway or Switzerland" if it withdrew from the EU.
In an interview with the New Statesman magazine published on Thursday, Jose Manuel Barroso said the UK's power was reliant on its membership of the union.
"I find it a litle bit ironic that some people are suggesting for Britain a role comparable to that of say Norway or Switzerland," he said.
"Norway or Switzerland are two marvellous countries, I very much admire, the most advanced countries in the world in fact with great qualities of life. But I think Britain is expecting a bigger role in the world than small countries."
Barroso was speaking to former Labour foreign secretary David Miliband who was guest editing the issue of the magazine.
His comments came as current foreign secretary William Hague is set to announce a "comprehensive audit" of EU legislation and its impact on the UK.
Hague is due to make a statement to the Commons at midday and the Financial Times reports that the audit is due to be complete by 2014, in time for the next election.
The plan will be seen by some attempt to appease the eurosceptic wing of the Conservative Party that wants to see powers brought back to Westminster from Brussels.
Last year David Cameron suffered a embarrassing rebellion when 81 Tory MPs voted in favour of holding a referendum on Britain's membership of the EU.
More recently the prime minister attempted to placate the rebels by indicating he would be prepared to hold a referendum in future, although ruled out holding one immediately.
In his interview with the New Statesman, the European Commission president said Britain's place in the world was now dependent on its ability to influence the policies of the EU.
"The fact that some are suggesting for Britain a role that's smaller than the one Britain already has today seems to me a little bit curious," Barroso said.
"When the prime minister of Britain meets the president of hte Untied States, or the president of China, he has a much stronger status and much stronger leverage because everbody knows Britain is a country that is very influential in the shaping of European policy.
He added: "Everyone in China knows that Britain is a decisive voice in the European policy and that its influence and its leverage it is much bigger because of that."
Barroso also warned that as 27 individual countries, the states of the EU were an "irrelevance"
"Where we are not united, where we have 27 different national politices we dont count, or we count very little," he said.