Ed Miliband should hold his nerve and not be "dragged along by the Ukip bandwagon" on Britain's membership of the European Union, former Labour minister and ex-European Commissioner Lord Mandelson told ITV News.
The Labour leader previously said he was against holding an in-out referendum under the terms proposed by Prime Minister David Cameron.
Lord Mandelson told Libby Wiener: "I think Ed Miliband is right to stand his ground but also to say that if there is in the future a need for, circumstances arising that require a referendum, then of course a Labour government would agree to that and put it to the British people".
More top news
Rain across much of the remainder of the country
Singer knocks Oasis from their 18-year hold on the top spot as her third album sells more than 800,000 copies in its first week of release
Francois Hollande has urged British MPs to support David Cameron's plan to launch airstrikes against so-called Islamic State in Syria.