Dr Dan Boucher was the Conservative candidate in Swansea East at the 2017 General Election.

One of the remarkable things about the unwritten British constitution is the way in which parliamentarians willingly stop short of pressing home what would otherwise be a political advantage because of unwritten conventions. Why is it that legislators stoically abide by these codes even when it costs them? Perhaps the answer lies in their effect. Enabling us to rise above the need for the aggressive application of law, they impart a certain constitutional flexibility and freedom. To some this might seem rather quaint, but it arguably brings, or at least should bring, a sense of dignity to our arrangements.

One such convention is the Salisbury-Addison Convention which has obtained since 1945. Named after the Conservative and Labour leaders in the Lords, it established the principle that the unelected chamber should not block a Bill at Second or Third Reading which was introduced in order to honour a manifesto commitment made by the elected party of government.

This principle makes good sense. Notwithstanding the constraints on its power, the Conservative-dominated Lords could have pressed home its right to vote down the Attlee Government’s legislation. Rather than taking this path, however, Conservative peers proactively recognised a moral obligation to respect the ballot box and, rather than waiting to be forced by law to have this freedom fettered, chose to rise to this challenge by embracing what was effectively a principled self-restraint. It is this capacity for principled self-restraint that does not seek the pressing home of legal rights just because it is possible to do so, but effectively pauses to ask whether it is right to press home such rights, which has helped to enable our political institutions to evolve out of difficulty.

The vitality of the British constitutional tradition, which famously finds it strength in being an ongoing growth rather than a finished creation, expresses itself not only by upholding existing conventions but also in developing new conventions, recognising the need for new manifestations of self-restraint as our political system evolves. In this regard, the constitutional convention that was inaugurated by Lords Salisbury and Addison in the 1940s is relevant to our present predicament.

The current difficulty arises from the fact that we have a referendum result pointing in one direction and a parliamentary majority pointing in another. Some might respond to this by saying that, as a matter of law, Parliament has the final say. On this basis, from a technical legal point of view, referenda are always advisory. Having a referendum cannot change the fact that any new law to implement a referendum result must be made by Parliament as our law-making body, not by the people in a mass plebiscite.

This technical legal reality, however, has to be held in tension with the political reality that if you give the people a referendum, don’t like their advice and then try to ignore it or tell them they were wrong, you create a huge political problem. This difficulty is greatly compounded in the current context, because the pamphlet the government sent to every household ahead of the referendum said: ‘The referendum on Thursday, 23rd June is your chance to decide if we should remain in or leave the European Union.’ The sense then was not that the referendum was being held to ask the British people for their advice, but rather to ask them to decide whether or not we should remain in the EU.

Some might respond to this by pointing out that the failure to be clear that the referendum was only advisory does not change the fact that in the British constitutional tradition it could only ever be advisory. Whilst this apparently purist presentation of constitutional doctrine may sound compelling, the truth is that the sovereignty of Parliament does not present a fatal problem for our evolving and unwritten constitution.

There is already an important sense in which, thanks to the Salisbury-Addison Convention, one of the Houses of Parliament has willingly embraced a convention of self-restraint in response to the democratic imperative. Once one House has used its sovereignty to willingly embraced self-restraint in this way, it follows that the other  could embrace self-restraint for the same reason. The only difference here is that the nature of the democratic imperative is more compelling in relation to a referendum mandate than in relation to a manifesto mandate – and thus the case for self-restraint by the Commons is stronger.

The Lords embraced voluntary self-restraint because it accepted that the government party is elected by the people on the basis of their manifesto. This then gives its election manifesto democratic legitimacy, even though it is highly unlikely that the winning party will have been elected because all its policies were liked equally. As Philip Norton observes: ‘Though an elected government may claim a mandate for whatever programme was embodied in its election manifesto, it cannot demonstrate definitively overwhelming support for any one particular proposal’.

For instance, whilst the electorate returned Margaret Thatcher in 1987 with a majority of over 100, it is doubtful that everyone who voted Conservative was doing so because they wanted the poll tax. By contrast, because a referendum is concerned with a very specific issue (notwithstanding debates about what different words may mean), it is possible to demonstrate express support for a particular proposal – in this case leaving the European Union.

In the context of the enhanced democratic mandate attending a clear public vote on a specific issue, the logic that called the Lords to exercise self-restraint applies even more to the Commons. Crucially, this would not result in changing the fact that Parliament remains sovereign. Parliament would remain so. It would freely choose to use its sovereignty to pass appropriate legislation to respect the referendum result, courtesy of a new convention of self-restraint that would develop (like the Salisbury Convention) to deal with the tensions resulting from the fact that a majority of people voted to leave the EU in the referendum while a majority of MPs would rather remain.

Given that the Salisbury-Addison Convention was named after the Conservative and Labour Leaders in the Lords, perhaps the time has come for a Leadsom-Vaz Convention in the Commons? That would hopefully restore greater dignity to our arrangements, shutting the door on revoking article 50 and hopefully opening the door to a greater determination to really honour the referendum result.