Originally published in The Times Red Box on 15 January 2019 and reproduced with permission

If as a result of today's 'meaningful vote' the UK-EU Withdrawal Agreement fails to come into force, we at the Hansard Society don't know of another case since 1864 where action by the UK Parliament led to such an outcome.

On that occasion the government felt obliged by parliamentary opposition to withdraw the Mutual Surrender of Criminals (Prussia) Bill, and the early extradition treaty it would have implemented did not come into effect.

The Withdrawal Agreement could join the international roll call of more famous treaties that failed, or at least ran into trouble, at a late stage as a result of opposition in a legislature, such as the US Senate's 1919 rejection of the Treaty of Versailles, the French National Assembly's 1954 refusal to ratify the European Defence Community, and the Walloon parliament's use of its power to stop Belgium's federal government from signing the EU-Canada Comprehensive and Economic Trade Agreement (CETA) in 2016.

The consensus seems to be that legally, procedurally and politically the Prime Minister could try again at least once to get the Withdrawal Agreement through, if that were her preferred course (although the scale of her likely defeat tonight might make a difference).

However, to state the obvious, when an executive has negotiated a treaty that it can't get through its legislature(s) at the first attempt, something in the process has gone wrong.

One of the ironies of today's debacle is that, by pre-Brexit law and precedent, the government did not need to give Parliament an explicit up-or-down vote on the Withdrawal Agreement at all.

Normally Parliament gets involved in treaty-making only when it is asked to pass any necessary implementing legislation — after a treaty has been signed. Strictly speaking, votes at this stage are votes on the legislation, not the treaty as such.

At the next stage in the treaty-making process, ratification, Parliament is not required to vote on its consent at all.

Given that it was the government's decision to grant Parliament a Withdrawal Agreement vote, it seems even more remarkable that it apparently took so few active steps to secure approval.

It is two days short of two years since the Prime Minister announced that Parliament would get a vote, in her Lancaster House speech; 588 days since she lost her House of Commons majority; and 204 days since the final form of the EU (Withdrawal) Act reached the statute book — and yet we are told that efforts to persuade opposition MPs not to vote against the deal got under way only in the past couple of weeks.

The kind of attempts now under way to discover what the Commons might support ought to have taken place much earlier in the process.

Imagine, for example, whether it might have made achievement of a ratifiable deal more likely if, a year ago, the government had sought explicit Commons endorsement for the Joint Report that put the negotiations on track for the backstop.

Thinking about these issues matters because Parliament's role in the making of the UK's post-Brexit treaties is still to be settled.

The Commons International Trade Committee called at the end of last year for the House to have a yes-no vote on the ratification of the UK's future trade agreements.

However, the probable rejection of the Withdrawal Agreement today could make for less enthusiasm about repeating the experiment of a definitive vote.

Decisions about Parliament's future role will also be shaped by assumptions about the likelihood of repeat minority government, and inter-party differences over trade and foreign policy.

But if the legislature is going to get a bigger role in future treaty-making, the experience of the Article 50 process could and should be taken as an opportunity to learn lessons, so that government and Parliament can ensure that today's likely failure does not happen again.