Mr Miliband admitted the victory for Nigel Farage’s party showed there was a “desire for Europe to work better for Britain” among the public.
But he stressed Labour had already set out its position on the referendum issue and would only back a national vote if a further transfer of powers to Brussels was being proposed.
The comments came amid growing unease over Mr Miliband’s prospects for winning the keys to Downing Street in the general election next May.
Despite a strong performance in London, Labour lagged behind Ukip in the European parliament poll and only just managed to beat the Tories into third place.
They also failed to take control of local councils in key areas.
Mr Miliband said the results showed Labour was making “progress” but had “further to go”.
Rejecting the idea that Labour could match the Tory promise of holding an in-out referendum in the next parliament, he said: “We set out our position for the general election on the European referendum.
“We will have a referendum if there is any transfer of powers from Britain to the European Union.”