Theresa May has paved the way to make her third and probably final bid to get her Brexit deal passed by MPs on Friday.

The government effectively booked a slot for a debate in the House of Commons but is yet to confirm that it will definitely bring forward a motion to be voted on.

The announcement by Leader of the Commons Andrea Leadsom caused confusion and consternation among MPs, who questioned if the government was attempting to somehow circumvent parliamentary rules constraining the government.

It comes as speaker John Bercow on Thursday reminded the government that he would not let them bring forward another vote on Ms May’s deal without there being substantial changes to the proposition on offer.

Ms Leadsom told MPs that the Commons will sit on 29 March – originally slated as Brexit day – to consider a motion on EU withdrawal but did not say the government would definitely bring forward a motion to be voted on.

When asked for more clarity by one Conservative MP she simply said: “My honourable friend should refer back to the business statement that I have just made.”

Despite MPs’ further efforts on both sides of the House to make Ms Leadsom elaborate on exactly what the plan is, she refused to give more detail.

The government faces two key challenges to passing Ms May’s deal – Mr Bercow’s opposition to an unchanged motion being brought back to the House and, secondly, a lack of support, in particular form the Northern Irish DUP.

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But they must also win the vote this week if they wish to secure the UK’s departure date as 22 May, as set out by the EU at the most recent European Council summit.

The ambiguity over whether there will actually on Friday be a vote, and on what kind of motion, could simply be the government reserving the slot in the parliamentary schedule while continuing to try and secure the DUP’s support.

Alternatively, it may be trying some kind of tactic to get round Mr Bercow’s ban on them bringing back Ms May’s deal repeatedly.

Some suspect that they will abandon the so called ‘meaningful vote’ currently needed to approve Ms May’s deal, and instead bring forward for a vote the actual legislation that would be required to lock the withdrawal deal in statute – making the motion of the vote different, while the effective outcome would remain the same.

Labour MP Chris Bryant said: “There seem to be some shenaniganating [sic] here. The leader of the House is being very coy which is not normal for her.

“She is normally more upfront. Maybe we could jut tease it out of her – is the plan just to bring forward the withdrawal agreement for the motion tomorrow?

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“Because if that is the case a lot of us in this House will think that does not meet the requirement of the Withdrawal Act.”

Ms Leadsom said what ever is brought forward would “of course meet UK law” but has not been finalised yet.

Across the road at the same time key ministers pleaded with MPs to back Ms May’s agreement at the annual British Chamber of Commerce (BCC) conference.

The prime minister’s deputy David Lidington said: “Now politicians of all political parties have a duty to put the national interest first so that we can put this controversy behind us and move on to a bright future for the British people.

“Every member of parliament, regardless of which political party he or she represents, regardless of which part of the country they serve, has to face up too to the fact that any deal, any aspiration for the nature of the future economic relationship between the UK and the EU, must include as a starting point the withdrawal agreement that has been negotiated with the EU.

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“If you believe in delivering the referendum result by leaving the EU with a deal then it is necessary to back the withdrawal agreement.”

Appearing at the conference shortly before Mr Lidington, cabinet minister Liz Truss made clear she wanted to see a Canada-style trade deal with the EU after Brexit.

But she also urged colleagues to first back the prime minister’s agreement in order to move on to the next phase of the negotiations over the UK’s future relationship with the bloc.