Brown has sent the treaty to parliament for ratification but Labour rebels and opposition members have tabled amendments calling for a referendum which will be put to the vote on Wednesday evening.
Many analysts believe the Lisbon treaty, which overhauls EU institutions, would be rejected if put to British voters. But Brown, buffeted by a bank crisis and government blunders during his first eight months in office, is determined not to call one.
Brown has a working majority of 67 seats. While rebels say 20-30 Labour lawmakers may defy the government, Brown's position appeared secure after Nick Clegg, the leader of the Liberal Democrats, the second largest opposition party, said his members would abstain.
EU leaders adopted the treaty after French and Dutch voters rejected a proposed constitution in 2005. Brown says it has been so watered down it no longer needs to be put to a popular vote.
Britain has a strong strain of Euroscepticism. The country stayed out of the euro and of the Schengen passport-free travel zone and negotiated a series of opt-outs from the Lisbon treaty.
Robin Shepherd, senior research fellow at the Chatham House thinktank, said the amendments had little chance of success.
If Britons rejected the treaty in a referendum, it would be an "enormous blow" for Brown, he said. "They will do everything they possibly can to avoid having a referendum."
The main opposition Conservative Party accuses Brown -- whose party trails in opinion polls -- of breaking his word by refusing a referendum on a treaty which it says is barely changed from the proposed constitution and gives away too many of Britain's powers to Brussels.
"Ninety percent of it (the constitution) is still there," Conservative foreign affairs spokesman William Hague told BBC radio. "The overriding issue of principle here is that a referendum was promised."
But Foreign Secretary David Miliband insisted the old constitutional treaty had been "abandoned". He said the Lisbon treaty would bring in much-needed reform of the EU's institutions and pose no threat to Britain's national interests.
The vote is due after 7 p.m. (1900 GMT). The Conservatives say if they lose in the lower house of parliament, they will take the battle to the upper house, where Labour does not have a majority.
Last Mod: 05 Mart 2008, 15:59