Brexit Secretary David Davis has been warned the country is on track for a “constitutional crisis”, after he confirmed that MPs will be able to amend the Government’s motion on the final EU withdrawal agreement.

The Brexit Secretary said the motion this autumn – which Prime Minister Theresa May has previously described as a “take it or leave it” choice – will relate to a political agreement expected to be reached with Brussels, rather than a full legal treaty.

But he told the House of Commons Exiting the EU Committee it remains the Government’s intention to have a treaty ready for signing immediately after the formal date of Brexit on March 29 2019.

Mr Davis confirmed that the motion could be amended by the House (Victoria Jones/PA)
Mr Davis confirmed that the motion could be amended by the House (Victoria Jones/PA)

The confirmation that the Government’s motion will be amendable opens the door to opponents of Brexit seeking to force a vote on a second referendum.

And Labour committee member Stephen Kinnock demanded to know what the Government would do if Parliament told ministers to go back and renegotiate the deal.

“To be clear, if the House amends the motion and instructs the Government to go back to Brussels and negotiate a different deal to the one that was put before us, the Government would respect the will of the House and go back to Brussels to do that?” asked Mr Kinnock.

Mr Davis did not rule out the possibility, but questioned how much “force” the Government would have in negotiations if it was “sent back with its tail between its legs by Parliament”.

He told the committee: “I’m not going to speculate on amendments that have not even yet been laid, let alone been passed by the House.”

Mr Kinnock responded: “Surely you must appreciate the risk of us heading towards a constitutional crisis here? And surely it’s the responsibility of the Government to have scenarios in mind so that it is ready to respond when the House does vote?”

Mr Davis played down suggestions that the Government’s proposals for the Irish border had run into the sand.

David Davis gives evidence to the House of Commons Exiting The EU Committee (www.parliamentlive.tv/PA)

Reports last week suggested that Brussels had dismissed as unworkable both of the options put forward by London, which would either see the UK collect customs tariffs on behalf of the EU or use technology to avoid delays at the border.

The reports sparked speculation that Brussels is trying to edge the UK into remaining in some form of customs union with the EU – something which committee Brexiteers regard as unacceptable, as it would prevent Britain from forging new trade deals elsewhere in the world.

But Mr Davis rejected committee chairman Hilary Benn’s suggestion that the UK solutions had been “emphatically” ruled out by Brussels, insisting that the EU was simply setting out an “opening position” in negotiations.

He played down the likelihood of defeat on an upcoming Commons vote on keeping the UK in a customs union, but suggested that ministers would “respect” MPs’ decision if that was the outcome.

Challenged on how the Government would respond to defeat, he said: “I’m not going to enter into hypotheticals. The Government always respects Parliament but I expect the Government’s policy to be upheld.”

Mr Davis was speaking ahead of a meeting on Wednesday afternoon of a Cabinet sub-committee dubbed Mrs May’s “Brexit war cabinet”, which will bring together senior ministers to drive negotiations forward in the vital coming months.

It is understood that the customs union is not on the formal agenda, but the issue is expected to test Cabinet unity in the coming weeks, with senior Brexiteers like Boris Johnson and Liam Fox understood to be wary of any concession.

Addressing the Brexit Committee, Mr Davis restated Government promises of a “meaningful vote” on the final deal, but confirmed that MPs and peers are likely at that stage to be presented with “a political declaration rather than a treaty draft”.

Asked by Mr Benn whether the motion would be amendable, the Brexit Secretary replied: “If you can tell me how to write an unamendable motion, I will take a tutorial.”

And pressed on whether ministers will regard the outcome as binding, Mr Davis said: “The Government is unlikely to put a vote to the House which it doesn’t intend to take properly seriously. If the House rejects the proposed negotiation, that negotiation will fall.”

Further votes could then be expected on any treaties which emerge from the process, which could include a separate pact on security and defence as well as the main agreement on economic relations, he said.

Mr Davis denied suggestions the Government was “winging it” over Brexit.

“No, we are not winging it, but we are having to accommodate different changes as we go along,” he said.

Theresa May’s official spokesman later said it remained the Government’s position that MPs will be offered a “take it or leave it” vote on the Brexit deal.

“We have been clear that this is a vote either to accept the deal or reject it,” said the PM’s spokesman.