Parliament needs to have a say on what happens next if the Brexit deal is rejected or if there is no deal

It was unusual for the UK to find a major constitutional issue – portrayed by some as the government versus the people – being played out in the courts. Other jurisdictions with constitutional courts are familiar with such debates. We rarely take to the law to resolve essentially political issues.

What became clear in the outcome, however, was that it was for parliament rather than the executive to take major decisions affecting people’s rights.

On Monday in the House of Lords, we will face a similar tussle. Is it for the government to decide that the choice is between the deal it has negotiated or a disorderly, chaotic exit? Or is it for Parliament to decide if the deal is adequate; and, if not, what should be done next?

At one level, the government admits it is not for it alone to decide. The prime minister has pledged that the “final agreement will be subject to a vote in both Houses of Parliament”.

What Ms May did not say was whether this vote would be binding on the government, nor whether it would have any legislative force. Indeed, each time we have asked about this, the clearer it has become that parliamentarians will be offered only a vote on a motion – and not a legal decision.

There are three reasons why this is not good enough.

Firstly, in our democratic system of government, parliamentarians – and in particular MPs – have both a right and the duty to determine what the government’s offer of a vote on the agreement should mean. Will it be before or after the European parliament has sanctioned the deal? Will it bind the government?

Secondly, the promise of a vote is only on the ‘final agreement’. With the prime minister maintaining that “no deal is better than a bad deal”, the offer would presumably not extend to a decision by the government to ‘walk away’ and let us fall out of EU membership.

The absence of a deal would mean no protection for UK citizens living in the other 27 states, no rights for EU citizens living here, a hard border between the north and south of Ireland, and immediate customs duties on the flow of goods. Any such outcome must be taken by parliament, not just ministers.

For any parliamentary approval process to be genuinely meaningful, this eventuality must be covered – and it is not by the government’s offer of a vote only on an agreement. This will not be the first time the Lords have asked for this. When the Bill authorising the government to trigger Article 50 was before us, there was a substantial majority for an amendment covering the ‘no deal’ outcome.

At the time, the Conservatives had a majority in the Commons and promptly overturned the amendment, while failing to give any commitment that Parliament should have a say on such a scenario. A void we seek to fill.

Thirdly, for the promised vote to be meaningful, Parliament would need to have a say on what happens next if the terms are rejected or if there is no deal. In either instance, it would be for the Commons to decide the next steps – not simply the government.

The stakes would be high. There is no point speculating now on what the best course of action would be. So at this stage, we should not close off any options for what might happen – more time to negotiate, a pause in the process or anything else.

That is why we have put our names to the amendment led by Conservative Peer, Viscount Hailsham, to be debated in the House of Lords on Monday.

We and others seek to ensure our country’s future should be determined by Parliament. It seems extraordinary that we should even have to argue that case. Even more so that we should be called mutineers or saboteurs for upholding democratic principles.