The motion put before Parliament this autumn on the final Brexit agreement will be amendable by MPs and its outcome will be binding on the Government, David Davis has said.

The Brexit Secretary said the motion – 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 said it remains the Government’s intention to have a treaty ready for signing immediately after the formal date of Brexit on March 29 2019.

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, or for Labour to demand that ministers go back and renegotiate a bad deal.

Giving evidence to the Commons Brexit Committee, 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.

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 told the committee that the technology to deliver a near frictionless border – including number-plate recognition, authorised economic operator systems and electronic pre-authorisation – already exists and the Government has started talks with potential suppliers.

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 to the utmost as the sub-committee meets 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.