The European Union's Lisbon Treaty was passed by Britain's parliament late Wednesday, hours ahead of an EU summit set to be clouded by Ireland's crushing rejection of it last week.
After a stormy debate in the unelected upper House of Lords, peers effectively ratified the treaty, giving the EU Amendment Bill a third and final reading without a vote.
The bill is set to go for Royal Assent by Queen Elizabeth II on Thursday morning, hours before Prime Minister Gordon Brown takes his place at the EU summit in Brussels.
Brown's government has defied critics who have called for a British referendum.
The Lisbon Treaty, which aims to streamline EU institutions after the bloc's expansion eastwards, was approved by members of parliament's lower House of Commons prior to last Thursday's referendum in Ireland.
All 27 member states have to ratify the treaty for it to take effect, but there have been increasing calls for it to be scrapped following its rejection by Irish voters.
Wednesday's Lords debate in London saw sometimes stormy scenes, while at least four protestors had to be ushered out of the public gallery. One protester, wearing a red t-shirt, shouted "the Irish have voted no."
Peers voted to reject a proposal to postpone the decision until October.
An opposition Conservative Party member of the Lords proposed an amendment which would delay approval of the treaty bill to take account of the changed situation after the Irish "No."
Lord David Howell, who sought to delay Wednesday's approval, said it was senseless to ratify the treaty if, as critics claim, it was killed by the Irish vote.
"If this treaty is truly dead... the next stage is pointless and a waste of time," he said. "If there are some changes to the treaty it is our duty to give the elected Commons a chance to reflect on the new situation."
Conservative Lord Richard Shepherd added: "Why can't you simply rejoice in (what) the Irish people have done?"
Brown was bullish earlier Wednesday, telling the Commons that Britain respected the Irish decision but pointing out that Dublin had asked for more time to discuss the way forward.
"They have not suggested either (that) they wish to postpone the ratification of the treaty of other countries or that they wish to stall the whole process," he said.
Any second vote by the Irish would be a matter for Dublin, he added.
"Just as we have respect for the Irish, we should have respect for the other countries that are processing the treaty and ratifying the treaty as well," he added.
Britain could, in theory, ratify the treaty and have it on the statute book by 11:00 a.m. (1000 GMT) Thursday, just before EU leaders meet in Brussels to discuss the ramifications of Ireland's rejection, the Foreign Office said.
The usually brief procedure could be complete before Brown travels to Brussels for the late-afternoon start of the two-day summit, a spokesman said.
The Lords' approval of the text agreed by the Commons bypasses the need for further "ping-pong" consultations between the two houses on the fine print.
The British ratification process, which until last week passed largely unnoticed by the public, has been put in the spotlight after events across the Irish Sea.
Czech Republic President Vaclav Klaus, a eurosceptic, questioned Wednesday why Britain was pushing ahead with the process.
Meanwhile, Bill Cash, a eurosceptic Conservative member of the Commons, is seeking a judicial review from London's High Court that the treaty is "incapable of ratification".
And a wealthy Tory supporter is also awaiting a High Court decision on his legal challenge to the government's refusal to hold a referendum.