It comes as it was reported that the EU is ready to consider a UK-wide customs arrangement as a way to avoid a hard border in Northern Ireland after Brexit.
Irish broadcaster RTE said this would need to be negotiated as a separate treaty and would not replace Brussels’ demand for a Northern Ireland-specific backstop to ensure the status quo along the Irish land border.
Reference to a UK-wide customs union arrangement would be included in the text of the UK’s withdrawal agreement, RTE’s Brussels correspondent Tony Connolly said.
Meanwhile, Downing Street confirmed that Theresa May has ordered a weekly update for ministers at Cabinet on the progress of preparations for Brexit both with and without a withdrawal deal.
The updates will be provided by Brexit Secretary Dominic Raab, who told ministers at Tuesday's meeting that "good progress" was being made, the Prime Minister's official spokesman said.
The Prime Minister told MPs on Monday the terms of Britain's withdrawal from the EU were 95% agreed but that the "sticking point" remained the issue of the Irish border.
However, she came under fire from critics on all sides in the Commons after she confirmed that she could accept a short extension to the transition period after the UK leaves in order to secure a final settlement.
Both Tory Brexiteers and Remainers expressed concern that it could leave the country trapped indefinitely in a transitional arrangement with no say in the rules governing it.
The latest display of backbench unrest came amid reports that the number of Conservative MPs submitting letters calling for her removal was approaching the 48 needed to trigger a no confidence vote in her leadership.
It follows warnings from Scottish Conservative leader Ruth Davidson and the Scottish Secretary David Mundell on potential compromises relating to the Irish backstop, particularly the suggestion that the post-Brexit transition phase could be extended to act as a ‘bridge’ to the future trading relationship.
Scottish Tory MPs have spoken out against any move that keeps the UK in the EU Common Fisheries Policy beyond the end of 2020.