MPs have just begun five days of debate on Mrs May’s withdrawal agreement with the EU, and the framework for future relations, ahead of the vote on Tuesday.
It means the government will have to come up with fresh plans within three days if Mrs May’s EU withdrawal deal is rejected by MPs next week.
It could also open the door to alternatives, such as a referendum.
The government lost by 11 votes, with 297 MPs voting with them and 308 against.
The government was expecting to have 21 days to come up with a “plan B” for Brexit if, as widely expected, Mrs May’s deal is voted down.
Labour’s shadow Brexit Secretary Sir Keir Starmer said: “The government’s decision to delay the meaningful vote has run down the clock and increased the risk of a no-deal Brexit.
“If the prime minister’s Brexit deal is defeated next week, she must return to Parliament as soon as possible and give MPs a real say on what happens next.”
Tory rebel Sarah Wollaston said Mr Bercow’s decision had upset those who believed that giving the PM three weeks to decide her next move if her deal was rejected was the best route to a “run the clock down, crash-out, hard Brexit”.
Commons Speaker John Bercow faced an angry backlash from some Conservative MPs over his decision to allow MPs to vote on the issue.
The MPs claim Mr Bercow broke Commons rules and ignored the advice of his own clerks.
On Tuesday, MPs, headed by former Tory ministers Oliver Letwin and Nick Boles, defied the government on an amendment aimed at making it more difficult to leave the EU without a deal.
The clashes in the Commons came as Theresa May launched a fresh push to convince MPs to back her Brexit deal.
The prime minister cancelled a vote on her deal last month at the last minute to avoid a humiliating defeat.
She is hoping new proposals on Northern Ireland will change enough MPs’ minds to save the deal.
Under the plans, the Northern Ireland Assembly would be given a say on new EU rules if the controversial border backstop comes into force after Brexit.
Ministers have also promised the UK Parliament more of a say in the next stage of negotiations over the UK’s future relations with the EU, which could begin immediately after Brexit.
Mr Barclay said he was keen for “closer and more targeted” engagement with Parliament amid criticism that the government has tried to sideline MPs since the 2016 Brexit vote.
- But Labour has said it will table a motion of no confidence in the government if Mrs May’s deal is voted down next week.p