Brexit: May facing constitutional crisis as Bercow says 'arguable case' government guilty of contempt of Parliament over legal advice

Speaker makes highly unusual statement in response to cross-party letter alleging ministers ignored will of Parliament

Theresa May is facing a full-blown constitutional crisis after House of Commons Speaker John Bercow ruled that there is "an arguable case" her government acted in contempt of Parliament.

The Speaker made the extraordinary statement in response to a letter from the other main political parties accusing the government of ignoring the will of Parliament in relation to the legal advice the Cabinet has received on Brexit.

In a highly unusual sequence of events, Labour, the SNP, the Liberal Democrats, Plaid Cymru and the Green Party joined forces to ask Mr Bercow to launch contempt proceedings after ministers refused to publish the full legal advice they had been given on Ms May's proposed exit deal.

In response, the Speaker granted an urgent debate on the issue, to take place on Tuesday. If passed, the motion could result in a senior government minister being suspended from the Commons.

Crucially, the DUP – whose votes Ms May relies on to maintain her governing majority – also backed the cross-party letter, making it likely that the motion alleging contempt will be passed unless the government backs down.

The dramatic move comes after ministers refused to obey a binding Commons vote saying they should publish all of the legal advice they have received on Britain's withdrawal from the EU.

Last month, the Commons unanimously passed a Labour motion calling for the release of any legal advice in full that had provided to ministers on the proposed withdrawal agreement and framework for the future EU-UK relationship.

However, the government responded on Monday by publishing only a 43-page summary of the advice and taking the unusual step of sending the attorney general, Geoffrey Cox, to the Commons to make a statement and answer questions from MPs.

The full legal advice given to ministers is understood to run to several thousand pages.

In a letter to Mr Bercow, the opposition parties and the DUP said MPs should be given a vote at the earliest opportunity on a motion accusing the government of contempt.

"We are writing to request that you consider giving precedence to a motion being placed before the House of Commons that the government has held Parliament in contempt," the letter said.

Referring to the motion passed last month, they wrote: "Neither a 'reasoned position statement' nor a document 'setting out the government’s legal position' constitute the final and full advice provided by the attorney general to the Cabinet. It does not comply with a motion of the House that you have ruled to be effective. It was the concession offered by the government during the debate, but it was rejected – and ministers made no attempt to amend or oppose the motion for debate.

"It is apparent to us – and we believe the overwhelming majority of the House – that the information released today does not constitute the final and full advice provided by the attorney general to the Cabinet. It does not comply with a motion of the House that you have ruled to be effective.

"We would now ask that you consider giving the House of Commons the opportunity to debate and consider this matter of contempt at the earliest opportunity."

Labour's shadow Brexit secretary, Sir Keir Starmer, said: "The government has failed to publish the attorney general's full and final legal advice to the Cabinet, as ordered by Parliament. We have therefore been left with no option but to write to the Speaker of the House of Commons to ask him to launch proceedings of contempt.”

Mr Bercow promised to give the letter his immediate attention and later told the Commons: "I have considered the matter carefully and I am satisfied that there is an arguable case that a contempt has been committed.

"I am therefore giving precedence to a motion to be tabled tonight, before the House rises, and to be taken as first business tomorrow. It will then be entirely for the House to decide on that motion."

MPs found to be in contempt of Parliament face the threat of being suspended or even expelled from the Commons. The motion to be debated on Tuesday is likely to focus on the actions of Geoffrey Cox, the attorney general, and David Lidington, Ms May's deputy, and whether they should be referred to Parliament's Privileges Committee.

As proceedings in the Commons drew to a close on Monday, Tory ministers appeared to be using delaying tactics to give the government time to table an amendment to the contempt motion. Foreign Office minister Alan Duncan spoke for 48 minutes during an adjournment debate, when ministers would usually be expected to speak for 15 minutes.

Ministers have insisted that the government's legal advice must remain private and argued that publishing it would set a dangerous precedent. Traditionally, expert legal opinion given to ministers has not been made public except in exceptional circumstances.

Giving evidence to the Commons Brexit committee on Monday, the new Brexit secretary, Stephen Barclay, said: "There are well-established conventions in terms of legal advice."

Ms May's official spokesman insisted the document published by the government was in line with the guarantees it had given to MPs.

He said: "It is a full-reasoned position statement as David Lidington set out in the House a few weeks ago," he said.

"We are meeting the commitments [Mr Lidington] made in the House of Commons when this matter was debated."

Addressing MPs later in the day, Mr Cox insisted it would not be appropriate to publish his advice in full.

The attorney general said he was convinced it would be contrary to the national interest to publish the full advice at a time when negotiations with the EU are ongoing.

"I would not take this decision if I did not feel [releasing the full advice] was contrary to all of our interests," he said.

"I am truly sorry that I am not in a position to disclose either the fact or the content of my advice, but I am doing so not to frustrate the legitimate interests of the members opposite or members behind me, but rather and only because I do believe it's against the public interest at a time when we're negotiating and at a time when these involve advice to a Cabinet which must be kept, for reasons of fundamental principle, confidential."

But responding for Labour, shadow solicitor general Nick Thomas-Symonds told the Commons it was unacceptable that ministers were refusing to publish Mr Cox's advice in full.

He said: "On 13 November in this House, the shadow Brexit secretary [Sir Keir] and I were both very clear that what was sought was the final and full advice provided by the attorney general to Cabinet on any completed withdrawal agreement, made available to all MPs in good time for the vote on the deal.

"Offers short of that, including the attorney general's statement today and a summary made by the government, were rejected, and the House passed the motion unanimously."

Raising a point of order with Mr Bercow, he said: "It is clear to me that the government has taken an unprecedented decision not to comply with the unanimous and binding decision of his House. Instead, they seem to be playing for time, hoping that contempt proceedings take longer than the timetable for the meaningful vote, and we as a House cannot allow this to happen."

Conservative Brexiteers and the DUP joined the opposition parties in calling for the full advice to be published.

DUP MP Nigel Dodds said: "As other honourable members have said, we need to see the actual legal advice as requested by this House, and that must happen."

And senior Tory Eurosceptic Sir Bill Cash said there had been five occasions in the 40 years when the attorney general's full advice legal advice to ministers had been made public.

Mr Cox "can and should" consent to his guidance being published in full, he said.

The attorney general's advice to the Cabinet is reported to make clear that the UK could end up stuck in the customs backstop "indefinitely".

He denied this when asked by MPs but admitted that the protocol, if it came into force, would continue to apply in international law unless and until it was superseded by the intended subsequent agreement that avoided the need for a hard border in Northern Ireland.

He said: "There is therefore no unilateral right for either party to terminate this arrangement. This means that if no superseding agreement can be reached within the implementation period, the protocol would be activated and in international law would subsist, even if negotiations had broken down.

"How likely that is to happen is a political question, to which the answer will no doubt depend partly on the extent to which it is in either party's interests to remain indefinitely within its arrangements."

Mr Cox said the customs backstop would be highly vulnerable to a legal challenge in European courts – a fact he said would put pressure on the EU to agree a deal with the UK on the future relationship.