“I’ll do everything possible to stop a No Deal Brexit”, has become the go-to soundbite for opposition leaders at Westminster. Indeed, they can now chant it in unison.

Surprisingly little critical attention is paid to the intellectual flaw in this proclamation – i.e. that it is categorically, demonstrably untrue.

Stopping No Deal has been within their collective and, in the cases of Corbyn and Blackford, individual powers for many months. All they had to do was lead their troops into voting through the deal which would have killed No Deal.

At this point, cries of “Ah, but…” tend to arise followed by explanations of why that was “impossible”. Oh, no it wasn’t. Not if “doing everything possible to stop No Deal” was ever the priority rather than a slogan of convenience. And is it is now?

Politics is about hard choices and the repeated choice made by Opposition parties was to vote down the EU-UK deal in the muddle-headed belief they could get something they actually wanted.

The problem was they wanted different things and, as is now blindingly obvious, had no clear road-map to achieving any of them. So they kept gambling. Something would turn up. Had not Sir Oliver Letwin promised them so?

Meanwhile, tribunes of the people linked arms with Europhile elitists to “defeat the Tory Brexit” – oblivious to the fact they were in the same division lobby as Jacob Rees-Mogg and co., who also wanted to defeat that particular “Tory Brexit” but with a clearer view of what might follow.

Things may change. Speaker Bercow may ride to the rescue. Judges may be aroused to block the proroguing of Parliament. Boris Johnson may decide that, crumbs, he really likes being PM and needs something that sounds like a new deal rather than the old one, but isn’t really.

However, as opposition MPs return to Westminster, the realistic assessment is that their successes so far have been in bringing No Deal into pole position by voting down the deal on offer and replacing Theresa May with Johnson. If that represents the fruits of effective opposition then I am the proverbial banana.

I voted to Remain, think the whole Brexit thing slightly bonkers, regard referendums as a plague upon the land (as Scotland was first to discover) but concluded as soon as the result emerged that it should be honoured because, sad to say, that is democracy.

My hope was that things would end up quite close to where they were before and had considerable faith in our diplomats to achieve that outcome – a Brexit the great majority of people could live with and, in some aspects, gain benefits from.

At the 2017 Election, that is pretty much where all Opposition parties stood. None – Labour, ScotNats, LibDems – committed to rejecting the result or holding a second referendum. That came later as conceit replaced caution among those who assumed the zeal of their own convictions could make the whole nasty business go away.

As this process evolved, I was daft enough to retain faith that one element of the debate would ultimately persuade enough MPs that supporting an imperfect deal was an awful lot better than betting the house against No Deal. My backstop was Ireland.

Surely, I reasoned, memories are not so short that the House of Commons will repeatedly vote down a deal which honours the Good Friday Agreement and recognises that, however dressed up, a barrier to free movement of goods and people within the island of Ireland simply must not happen.

I was hopelessly wrong and that is where I find the hypocrisy of “I’ll do everything possible to stop No Deal” particularly offensive. When they had the chance, most MPs did not even regard safeguarding peace within Ireland a sufficient reason to compromise over a deal with that specific imperative written into it.

Of course, the European Research Group would dismiss the Irish backstop on grounds that the Irish tail must not wag the British bulldog. It is harder to understand why others, with a less imperial view of history, have escaped censure for failing to acknowledge Ireland’s peace as the starting point for any agreement, rather than an alien imposition or optional extra.

It may be unfashionable but I pay tribute in this regard to Mrs May. Having accepted there could not be a trade border within Ireland, she stuck with that principle to her own personal cost. This involved an enormous irony since the only political party on the island of Ireland which opposes the backstop is the DUP, to which Mrs May owed her majority.

Consider in contrast the cynicism of other leaders who treated the Irish backstop as just another pawn in defeating the government and excoriating the deal on offer. Could Jeremy Corbyn not have taken advice from Gerry Adams? Could the Celtic Nationalists not have shown solidarity with their Irish cousins?

Instead, they voted repeatedly with the ERG to defeat the deal that would have wiped No Deal off the map, removed the Irish border issue from the political agenda and underpinned a peace that already seems disturbingly vulnerable, as the republican fringes start to stir. To me, that would have been a deal worth having.

The miracle of the Good Friday Agreement was to separate two issues hitherto regarded as synonymous – the Border and Partition. The Border, for practical purposes, no longer exists which papers over the fact that Ireland is still divided. That accommodation demands vigilance rather than exposure to unnecessary risk.

After 20 years, with power-sharing in abeyance and tribal politics entrenched, acceptance of the historic compromise depends more than ever on no faction having a rationale, however misguided, for blowing it up. Yet that is the fire with which MPs are playing.

When they return to Westminster, they should try squaring their consciences with their intellects. If they will do “everything possible to prevent No Deal” then they should swallow hard and support a deal – not least, and perhaps most of all, because it contains an Irish backstop.

Rt Hon Brian Wilson is a former Labour MP and UK Trade Minister who lives on the Isle of Lewis and is chairman of Harris Tweed Hebrides.