It cannot be easy being Keir Starmer. A cerebral, rational lawyer with a forensic mind who entered politics just as populism was infecting it badly. A man used to executive authority, built more for government than opposition. With a place at the top table as shadow Brexit secretary but viewed on that issue, and much else, with considerable suspicion by true Corbynista believers in the leader’s inner circle. Having to forge a position that straddles the historic Euroscepticism of Jeremy Corbyn and the posh boy revolutionaries who surround him, the overwhelming pro-Europeanism of Labour members whom the leadership says it listens to, and the “will of the people” as expressed on one day in June 2016.

It was these competing pressures that led Starmer and Corbyn to arrive at a position defined as “constructive ambiguity”. In Theresa May’s disastrous election campaign, the ambiguity seemed to work well. Leavers sensed Corbyn was basically on their side. Remainers saw Labour as the only credible route to blunt May’s push for hard Brexit. The party was able to shift the focus to other issues, and allow the elephant in the room to fade into the background.

Constructive ambiguity was a phrase Tony Blair often used to describe our approach to negotiating peace in Northern Ireland. But there came a point, as he put it, when that strategy had to be replaced by “acts of completion”. Similarly, the latter-day version of constructive ambiguity has run its course and must be replaced by acts of decision.

Just as the government is finally having to confront some difficult choices, so is Labour. And facing both ways will hold neither electoral appeal nor intellectual credibility, not least because Starmer set six tests against which he said May’s Brexit deal would be judged, and it is becoming ever clearer than none of them are being met.

Does it ensure a strong and collaborative future relationship with the EU? It will certainly be weaker and less collaborative than now.

Does it deliver the “exact same benefits” as we currently have as members of the single market and customs union? No, and none of the deals on offer will do so.

Does it ensure the fair management of migration in the interests of the economy and communities? Highly unlikely and, looking at the Windrush scandal, would we trust May to deal with the rights of EU migrants in Britain and UK migrants in Europe?

Does it defend rights and protections and prevent a race to the bottom? A race to the bottom is precisely what many Brexiteers want.

Does it protect national security and our capacity to tackle cross-border crime? Not according to anyone I know who is working in that field.

Does it deliver for all regions and nations of the UK? No, and the government impact assessment papers make that perfectly clear.

Even at this stage, it is impossible to imagine the deal that could be secured from the current “screwed-up … botched … delusional … shambles” – as the Vote Leave director Dominic Cummings calls the negotiations – that would not be opposed by a “jobs first” Labour frontbench.

As a hardcore remainer, who believes that if you believe something will damage the country you should seek to prevent it, I welcomed the Starmer tests precisely because I could see no way they would be met, and therefore no way Labour could support the Brexit put before parliament. Add a reasonably sized Tory rebellion to a Labour whip against a deal that failed to pass the tests, then the government is defeated, a crisis ensues and, who knows, it may suit May, and parliament, to put the deal to a people’s vote.

However, though there seems to me to be a compelling logic that moves from failure to meet the tests to a three-line whip against the deal, it does not appear to be shared by the normally hyper-logical lawyer. Indeed, you will have to look long and hard to find him on the record as saying Labour will vote against a deal that fails to meet those tests. Refusing to support is not the same as opposing. And at last week’s meeting of the parliamentary Labour party, when Starmer projected himself as the driver of step-by-step shifts in Labour’s position, MPs such as Mary Creagh pointed out that it had taken persistent and steady rebellion to get the leadership to move at all.

Though the MP Owen Smith was sacked for daring to voice opposition to one part of Labour’s Brexit strategy, Barry Gardiner survived, and continues to be one of the few Labour faces allowed on TV, despite dismissing the Starmer tests – surely the key plank of the strategy – as “bollocks”.

But now Starmer himself has given the impression that Labour has no intention of using any vote in parliament this year to block a Brexit deal, even if it obviously fails his tests.

“In my heart of hearts,” he told the Fabian Society, “I don’t think we’re going to know what “out” looks like until the end of the transition period. I really don’t. I wish I thought otherwise, but I don’t. I think that out will only come into full shape probably at the earliest 2021.”

I always feared the transition was a trap and this suggests Labour intends fully to fall into it. This must be music to the ears of Brextremists who just want to get to March 2019, because they know that once the flag comes down there is no chance of it going back up again for a generation or more, whatever the mess that ensues.

To compound the fault, Starmer spoke in the context of seeking to discourage supporters of a people’s vote on the final deal. So, if Labour will not vote against the deal in parliament, even if the tests are failed, and he won’t support a people’s vote on the deal, it puts Labour in much the same position as the government and the Brextremists within it. Whatever the costs, whatever the consequences, we are out. And the fine talk that “we would negotiate a better deal” will have to change tense subtly, and irrelevantly, to “we would have negotiated a better deal”.

It leaves me with the uneasy feeling that Starmer is taking us for fools. He risks enabling Brexit without the people being given a final say on the deal on the utterly spurious grounds that no one will know the full consequences of leaving Europe until after we’ve left. A lawyer as good as Keir should be embarrassed to make such an argument. A Labour party that was founded to stand up for working people should be ashamed if it helps facilitate a hard Brexit that will hit those people hardest of all.

Labour members deserve better than this. We deserve a party leadership that is willing to fight the Tories on their disastrous approach to Brexit and which does so in words of clarity and directness, full on.

Jeremy Corbyn still has enough credibility and celebrity to get a great reception when speaking to students in Northern Ireland. But there is every danger of a hard border, which he insists will never be, materialising with the hard Brexit he is failing properly to oppose.

The government is wide open to be torn apart on Brexit, which is shaping up to be biggest con job since the South Sea Bubble. A government that insists on pressing on with such a shoddy scheme will never be forgiven. But nor will an opposition that lets them get away with it.