British MPs will on Wednesday begin five days of debate ahead of a historic delayed vote on Prime Minister Theresa May's Brexit deal, a day after giving her a stinging blow aimed at preventing Britain from crashing out of the bloc with no agreement.
Lawmakers will vote next Tuesday on the agreement that May has negotiated with the EU over the last 18 months, which faces daunting opposition as the clock ticks down before Britain leaves the EU.
The prime minister has warned rebels in her own party that defeat will lead to a no-deal Brexit, or no departure from the bloc at all.
But in a major setback Tuesday that presages likely defeat in next week's vote, MPs approved an amendment that will curtail the government's tax powers in case of a no-deal Brexit.
David Lidington, May's effective deputy, called the House of Commons defeat "inconvenient" yet ineffectual and insisted the government remained focused on winning approval for the prime minister's plan.
"We are focused on getting any possible vote in favor of the PM's deal," he told BBC radio.
"I don't think the British public are served by fantasies about magical alternative deals.
"The choice the people have is this deal or no deal, or - as some MPs advocate - to reverse the 2016 referendum entirely."
However, ardent Brexit supporters who favor a clean break when Britain is scheduled to leave the EU on March 29 look set to rebel over fears the draft divorce deal could lead to some kind of customs union with the bloc.
UK Prime Minister May has already pulled the vote once with defeat looming.
A loss for the government would plunge Britain into "uncharted territory," according to May.
She is still seeking assurances from the EU on the most controversial elements of the Brexit deal relating to Northern Ireland, in a bid to convince critics to back the agreement.
These assurances are set to be delivered to lawmakers before they vote, although not before they start their debate on Wednesday.
"The work to secure those assurances is ongoing. I think what's important is that if we are to secure assurances, MPs are aware of what they are before the vote takes place," a Downing Street spokesman said.