If supported by a vote in parliament, the move would be embarrassing for a leader who has worked hard to keep much of Britain’s Brexit negotiations secret, especially the debate on customs arrangements with the European Union.
The government tried late on Tuesday to rebuff Labour by saying it would soon publish its vision for Brexit, setting out over more than 100 pages its plans for everything from fishing to finance to security cooperation.
May is under pressure at home and in Brussels to move forward with talks on Britain’s divorce from the EU that have all but stalled, but is struggling to unite her cabinet of ministers around a single customs proposal.
Using a rarely used parliamentary device called a “humble address”, Labour will call on Queen Elizabeth to give directions that “all papers, presentations and economic analysis” from January be offered up to the House of Commons, the lower house.
On Tuesday, Labour’s Brexit policy chief, Keir Starmer, suggested that with a weakened May unable to decide on a customs proposal, “she should give parliament the information to let it decide”.
May has divided most of her cabinet into two groups to try to improve the two proposals and come to a conclusion over which is best placed to prevent a return to a hard border with EU member Ireland and ensure trade moves as freely as possible.
They have been meeting regularly, but a meeting of her so-called Brexit war cabinet on Tuesday again ended without agreement. Ministers have suggested that any decision could take weeks.
But EU negotiator Michel Barnier said on Monday that no significant progress had been made in the Brexit talks since March and warned London that time was running out to seal a deal by October to prevent Britain crashing out of the bloc.
By promising to publish a White Paper, a policy document that sets out proposals for future legislation, next month, the government hopes to set out its stall before the next summit of EU leaders on June 28-29. But without an agreement on customs, those plans are as yet incomplete.
It is “an opportunity to set out clearly to both a domestic and an EU audience the reasoning behind our approach”, Brexit minister David Davis said.
Reporting by Elizabeth Piper; editing by Stephen Addison