Any new European treaties would have to be ratified by a referendum under plans put forward by the Conservatives.

Shadow foreign secretary William Hague told party members at their conference in Blackpool that the Tories would make a vote necessary by law.

In a speech dominated by Europe, he said the government's claim that the EU treaty is fundamentally different from the failed EU constitution was "one of the most bare-faced and deliberate misrepresentations in the modern annals of political deceit."

Party leader David Cameron had earlier described Gordon Brown's failure to hold a referendum as "one of the most flagrant breaches of trust" in British politics.

The Conservatives argue that the government should honour its 2005 manifesto commitment to hold a referendum on the constitution, which was rejected by voters in France and Holland.

The prime minister has repeatedly dismissed opposition calls for a vote, arguing that the treaty is a fundamentally different document and does not give up key UK powers.

Hague said: "Labour promised a referendum on the EU constitution at the last election.

"Without holding one on a treaty so similar, Gordon Brown has no democratic mandate to surrender the rights and powers of the people of this country."

In reference to an anticipated November election, Hague said: "A Conservative government elected this autumn will hold a referendum on any EU treaty which emerges from the current negotiations.

"And I can tell you today that we will go further: The next Conservative government will amend the 1972 European Communities Act, so that if any future government agrees any treaty that transfers further competencies from Britain to the EU a national referendum before it could be ratified would be required by law.

"And so, as we campaign - all of us here - for the referendum the people of our country were solemnly promised, we are fighting not only for them to have their say now but for them always to have their say; to extend their power over their own lives not just for today but permanently into the future."