David Cameron has said that he will renegotiate Britain's relationship with the EU with the determination of Margaret Thatcher if he comes to power.
He has ruled out a full referendum on the Lisbon Treaty - which he had promised - if it is ratified by all 27 EU member states before the general election.
The issue of Europe has so far dominated events in Manchester, where the Conservatives are starting their annual conference.
Ireland voted "yes" to the Lisbon Treaty on Saturday, and Poland and the Czech Republic have indicated that they will ratify it within months. The Czech president, Vaclav Klaus, made a statement that made it clear that he thought it was too late for Britain to halt the Lisbon Treaty.
He said: ""There will never be another referendum in Europe. The people of Britain should have been doing something much earlier and not just now - too late - saying something and waiting for my decision."
Cameron said that a referendum would still be held if the treaty was not ratified by all member states in the event of a Conservative government, but the refusal to commit to a referendum even if the treaty is ratified has infuriated some Tories.
It is understood that Cameron has accepted that it will be impossible to unpick some of the main institutional changes to the EU contained in the treaty.
However, he has toughened his language on Europe, saying that he will instead launch a campaign to renegotiate its relationship with Britain.
This will include repatriating social and employment powers and having greater power over justice and home affairs than there is under the Lisbon Treaty.
He will also warn that a Tory government would take a hardline stance if their demands were not met, such as blocking the next round of EU treaties to allow Iceland and Croatia into the union.
In a further twist, Boris Johnson appeared to take a different line when he told the Mail on Sunday that he wanted a referendum to give voters the chance to block Tony Blair from becoming president of the European Council, a role which the treaty will introduce.
Johnson and Cameron claimed there was no rift between them. Johnson apparently thought he was toeing the line because Cameron has previously declined to clarify his position in the event of the treaty being ratified by all 27 member states.
The foreign secretary David Miliband accused Cameron of a "real failure of leadership" after Ireland ratified the treaty.