Lord Mandelson has said the Labour party would be "foolhardy" to offer any sort of in/out referendum on the EU - but said one might be needed to see if the public wanted to join a reformed single currency.
The former cabinet minister and EU trade commissioner said he did not believe David Cameron would commit to a public vote because for the Tories it would spell "political suicide by splitting them from top to tail.
"I do not think the Labour Party would be so foolhardy as to have a 'clear the air' referendum," he said.
But in five to 10 years, if the eurozone was reformed and there was a "gravitational pull of power, decision making and policy" among the member states that belonged to it, voters might want to "reconsider whether we want to join the core".
"It will not be for government or a political party or a combination of political parties to make that decision; it will be one for the British people," he added.