By Paul Taylor and Mike Peacock
BRUSSELS, Feb 26 (Reuters) - European Commission President Jose Manuel Barroso said on Tuesday he was convinced Britain would vote to stay in the European Union if a promised referendum takes place, despite opinion polls showing a plurality in favour of leaving.
However, he also told a Reuters Summit on the future of the euro zone the EU could not revise its policies just because one country was thinking of holding a vote on continued membership.
Prime Minister David Cameron promised last month to give Britons an in-out choice on whether to remain in the 27-nation bloc if he is re-elected in 2015, after trying to negotiate a reform of EU policies to meet British concerns.
"Knowing Britain a little bit, and knowing how important the business community is and the role that different parts of British society can have on this open debate, in case there is a referendum, I am confident that Britain will remain a member of the European Union," Barroso said.
Cameron's Conservative party wants to "repatriate" to London EU powers over a range of social, employment, justice, police and fisheries policies. His Liberal Democrat coalition partners and the main opposition Labour Party both support EU membership.
However, the Eurosceptical UK Independence Party and some dissident Conservatives favour outright withdrawal from the bloc, and latest opinion polls show about half of Britons want to leave while just a third say they would vote to stay.
Barroso lauded Britain's contribution to Europe, notably in promoting the single market for goods and services, the EU's eastward enlargement, its open trade policy and its leading role in the fight against climate change.
But he conceded it was a "reluctant partner" when it came to institutional issues.
The head of the EU executive, which proposes legislation and enforces European rules, said he was convinced ways would be found to enable the 17-nation euro zone to move forward in closer integration while keeping Britain on board.
He cited as an example an agreement in December to create a single banking supervisor for the euro area, in which solutions were found to accommodate British interests even though London has no intention of joining a European banking union.
Barroso said he understood some British concerns about EU authority stretching into too many areas of national life, and the EU should be self-critical, assess its performance and make improvements that could respond to those concerns.
But he added: "With the greatest of respect for Britain as a member state, we cannot now because one country has a referendum, or signals the possibility of having a referendum, put into question all of our policies because of the concerns of that one country." (Writing by Paul Taylor, editing by Mike Peacock)