Gordon Brown faces a battle to get the EU treaty through Parliament after it was agreed by EU leaders in Lisbon.
Mr Brown insists there is no need for a referendum
The prime minister ruled out a referendum saying he had already "safeguarded the national interest" with "red line" opt-outs in key areas.
But Tory leader David Cameron accused him of treating Britons "like fools" and pledged to fight for a referendum when MPs debate ratification next year.
It has to be ratified by all EU states before coming into effect in 2009.
Mr Brown said he wanted the "fullest possible Parliamentary debate" on the treaty.
"I believe that debate will show that we have at all points defended the British national interest," he told reporters earlier.
Mr Brown is understood to have set aside up to three months to ratify the treaty, and has briefed colleagues to expect a protracted battle starting in the New Year.
BBC News 24's chief political correspondent James Landale said Labour may be hoping a lengthy debate on the EU treaty will kill off demands for a referendum by making it "confusing to many people and they will switch off from it".
The treaty deal was struck after late-night wrangling between the 27 heads of state and government over the number of Italian MEPs and Poland's voting strength in the reformed EU.
Mr Brown told reporters it would rule out further institutional change in Europe "for many years to come".
He said EU leaders could now concentrate on discussion about jobs, prosperity, the environment and "how we can respond to the changing needs of the world economy in the interests of the citizens of Britain".
UK opt outs in key areas like human rights, tax and benefits, foreign policy and justice meant there was "no fundamental change" to British sovereignty, said Mr Brown.
But David Cameron warned the treaty would mean a "significant transfer of power" to Brussels and he believed it should be put to the public, rather than just being scrutinised by MPs.
"Gordon Brown made a promise to hold a referendum on the EU Constitution.
"This treaty is almost exactly the same as the Constitution and they have broken their promise. We will fight for the referendum in the House of Commons and we will try to make sure he keeps his promise to the British people.
He added: "Just about every MP in Parliament was elected on a promise to hold a referendum.
"Gordon Brown has no democratic mandate to agree to this treaty without the British people having their say.
"We are keeping our promise - he should keep his."
Foreign Secretary David Miliband has said he "fully expects" there to be a vote on whether to hold a referendum when MPs debate the treaty.
A number of Labour MPs - including former Europe Minister Keith Vaz and former minister Gisela Stuart, who helped draw up the original constitution - also want a referendum, setting up the prospect of a backbench rebellion.
The Conservatives are also expected to use every Parliamentary tactic at their disposal to block the ratification process, in a repeat of debates on the Maastricht treaty 15 years ago.
The Liberal Democrats are likely to vote with the government on the question of a referendum - although much will depend on their new leader, who will be elected in December.
Nick Clegg, favourite at the bookmakers to land the job, said he did not want a referendum, as the reform treaty was a "modest" document compared to previous EU treaties.
UK Independence Party leader Nigel Farage called for a referendum on the whole question of British membership of the EU.
"It is over 30 years since the British people were asked. When they were asked in '75, they were told that we could be part of a European Community that was about free trade and friendship," he told BBC Radio 4's Today programme.
"Well, here in Lisbon we have agreed a treaty that makes the European Union a country. A country called Europe now exists once this treaty goes through - there is no legal debate or argument about that."
EU governments are due to formally sign the reform treaty - which has been negotiated over two years since the constitution was rejected - in December.
Over the next 12 months it would then be ratified by the individual parliaments, to come into effect on 1 January 2009.