MPs will vote later on whether to block the UK from leaving the EU without a deal on 29 March, after again rejecting the PM’s withdrawal agreement.
The deal was defeated in the Commons on Tuesday evening by 149 votes.
Meanwhile the UK government has said it will cut tariffs on a range of imports from outside the EU and introduce measures to avoid a hard border in Northern Ireland in a no-deal scenario.
The EU said no deal plans were “more important than ever” after the defeat.
Numerous EU leaders expressed their dismay after MPs voted by 391 to 242 votes to reject Mrs May’s deal.
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On Wednesday morning the government announced that most imports into the UK would not attract a tariff in the event of a no-deal Brexit.
Under a temporary scheme 87% of imports by value would be eligible for zero-tariff access – up from 80% at present. Tariffs would be maintained to protect some industries, including agriculture.
The government also announced it will not introduce any new checks or controls, or require customs declarations for any goods moving from across the border from Ireland to Northern Ireland if the UK leaves the EU without a deal.
The decision to drop all checks to avoid friction at the UK’s land border with the EU will be temporary while longer term solutions are negotiated.
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What is Wednesday’s vote on?
Mrs May, who is currently chairing a cabinet meeting, has said Tory MPs will get a free vote on Wednesday evening’s motion.
That means ministers and MPs can vote with their conscience rather than following the orders of party managers – an unusual move for a vote on a major policy.
Wednesday’s no-deal debate will begin after Prime Minister’s Questions and Chancellor Philip Hammond’s Spring Statement economic update.
MPs are expected to vote on the government motion, which says: “This House declines to approve leaving the European Union without a withdrawal agreement and a framework on the future relationship on 29 March”, at about 19:00.
If no-deal is rejected, MPs will vote on Thursday on delaying Brexit by extending Article 50 – the legal mechanism that takes the UK out of the EU.
The EU has said it would need “a credible justification” before agreeing to any extension. Leaving the EU in 16 days’ time remains the UK’s default position under the law.
MPs call for alternative proposals
Labour has called for no-deal to be “taken off the table” – and said it would continue to push its alternative Brexit proposals, including a customs union.
Shadow business secretary Rebecca Long-Bailey told BBC News Parliament would increasingly “set the agenda” if the government was not in control of events.
She said No 10 should consider giving MPs a free vote on the full range of options for the UK’s relationship with the EU – more details of which will emerge later in the form of MPs’ amendments.
The PM had made a last-minute plea to MPs to back her deal after she had secured legal assurances on the Irish backstop from the EU during late-night talks in Strasbourg on Monday.
But although she managed to convince about 40 Tory MPs to change their mind, it was not nearly enough to overturn the historic 230 vote defeat she suffered on the same deal in January.
Cabinet divided on next move
What isn’t clear is how the prime minister actually intends to dig herself out of this dreadful political hole.
Some of her colleagues around the Cabinet table think it shows she has to tack to a closer deal with the EU.
Some of them believe it’s time now to go hell-for-leather to leave without an overarching deal but move to make as much preparation as possible, and fast.
Other ministers believe genuinely, still with around two weeks to go, and an EU summit next week, there is still time to try to manoeuvre her deal through – somehow.
Speaking after the defeat, she said MPs would have to decide whether they want to delay Brexit, hold another referendum, or whether they “want to leave with a deal but not this deal”.
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She will tell MPs whether she will vote for no deal or not when she opens Wednesday’s debate.
A No 10 spokesman said she did not discuss resigning after her latest defeat because her government had recently won a confidence vote in the Commons.
Leading Tory Remainers and Brexiteers, including Dominic Grieve and Boris Johnson, have suggested the prime minister’s deal is now “finished” and other options must be brought forward.
Members of the European Research Group of Conservative MPs have tabled an amendment that would see the UK leave without a formal agreement, with the backstop being replaced by alternative arrangements and a series of “standstill” economic arrangements until the end of 2021 to minimise disruption.
Steve Baker, the organisation’s vice-chairman, told BBC News the proposal – which would see Brexit delayed until 22 May – was “eminently reasonable” and was supported by the Democratic Unionists and former Remain ministers like Nicky Morgan and Damian Green,
But Tory former minister Nick Boles said this would amount to a no-deal exit and the EU would not agree to it.
The EU’s chief negotiator, Michel Barnier, has said the current impasse “can only be solved in the UK” and MPs must decide what they want rather than what they don’t.
UK MPs to vote on stopping no-deal Brexit