David Cameron was struggling to maintain party discipline as divisions over Europe marred the opening day of the Conservative conference.
The Tory leader has tried to rally his party to demand a referendum on the Lisbon Treaty. It is yet to be ratified by all EU members but Mr Cameron is refusing to say how he would act if it is approved before the election. But the policy was under strain as Eurosceptics stepped up demands for a referendum under all circumstances.
Boris Johnson, the Mayor of London, suggested "key parts" of Lisbon could be put to the voters even if the document had been ratified.
Andrew Rosindell, a shadow Home Affairs spokesman, also said people had a "right to expect" a referendum "whatever the circumstances". Mr Rosindell later issued a statement insisting the leadership had his support.
Sir Malcolm Rifkind, the former foreign secretary, warned it would be "pointless" to stage a referendum once the treaty had been ratified.
Kenneth Clarke, the pro-European shadow Business Secretary, also appeared to question whether a referendum would ever be held – and to hint he would join the campaign for a Yes vote if it was. Mr Clarke later denied this interpretation of his remarks.
In a sign of Tory grassroots dismay over their leader's position, shadow minister Greg Clark was barracked by activists at a fringe event when he sought to defend it. Mr Cameron also suffered the embarrassment of a key European ally warning he would regret his stance on the Lisbon Treaty.
The conservative Swedish prime minister, and EU council president, Fredrik Reinfeldt, said: "As far as I'm concerned, [Britain] is a country which has already ratified the treaty." Mr Reinfeldt told Le Monde he admired Mr Cameron but added: "We disagree on the referendum. Making such a promise will not help him at all as Britain's probable future prime minister."