Unsurprisingly, the Labour leadership is scathing about the government’s Brexit strategy, mocking the internal divisions and delusions that fuel ministerial statements. There is, though, one big problem with its attempt at mockery: Labour’s position on Brexit is more or less the same as the government’s. As far it has a position, Labour also wants to have its cake and eat it. The party seeks to be out of the EU by 2019 and yet have tariff-free “access” to the single market and the customs union. Sometimes Labour does not rule out full membership of the single market and the customs union; sometimes it does.

I fully appreciate the case for evasiveness in relation to Europe. Labour was so constructively ambiguous at this year’s general election that it managed to attract angry remainers and determined Brexiteers. Nor is there anything new in such evasiveness. In the mid-90s Tony Blair managed to be in favour of the euro and opposed to it. More than 20 years earlier, Harold Wilson supported and opposed the UK’s membership of the EU depending on whether his stance would unite or destroy his party.

Dissembling over Europe is sometimes necessary. I even understand Jeremy Corbyn’s reticence during the Brexit referendum. Why should he have gone all out for a remain vote, which a mountain of commentators would have hailed as a triumph for Cameron/Osborne, when he had deep reservations about the EU?

But there are also phases in the eternal Europe saga when a party’s self-interest demands clarity. Labour has reached such a junction now. Virtually every time a senior frontbencher speaks out on the issue he or she is reduced to nervy incoherence. Recently it was the turn of the shadow international trade minister Bill Esterson, who could not answer obvious questions about Labour’s approach. Earlier in the summer the frontbencher Barry Gardiner ruled out membership of the customs union, only to be told by other colleagues that membership remained an “option”. Such “clarifications” that openly contradict other frontbenchers’ assessments are becoming chaotically frequent for several reasons.

The most obvious is that while evasiveness can be convenient, it can also lead to confusion. Labour’s position is unsustainable. It aches to expose the recklessness of the Tories in relation to Brexit and plans to oppose some of the vast layers of Brexit legislation that will overwhelm forthcoming parliamentary sessions. Yet it does not have a clear alternative Brexit strategy.

The government is not wilfully heading towards a cliff’s edge. It is doing so because there is no alternative route

The government is not wilfully heading towards a cliff’s edge. It is doing so because there is no alternative route. Trade secretary Liam Fox is right to argue that the UK must leave the customs union after March 2019 or it will not be free to negotiate alternative trade deals. The flaw in his argument is that he will not have the time to secure such deals during a short transition.

Meanwhile, the EU will not allow Britain to leave the customs union and remain part of it, which is the government’s current fantasy position. A hard Brexit is unavoidable. As Vernon Bogdanor argued in the Guardian this month, even paying for access to the single market is not a soft option but a humiliation, with the UK becoming a powerless colony of the EU.

In reality, there will be only two options for Labour to contemplate over the next 12 months: the government’s version of Brexit, or no Brexit. At some point Labour will have to choose. To be more precise, when the government puts its final deal to parliament, Labour will have to support or oppose it. As Labour has argued that no deal would be the worst of all outcomes and there would be no time for an alternative Brexit to be negotiated, Labour would have to put the case for staying in the EU as a better option than the Brexit deal on the table.

In order for them to have the freedom to contemplate such a position, Corbyn would need to raise the option of remaining in the EU sooner rather than later. Only then would shadow cabinet members be able to argue with coherence and credibility. Instead of their current position, which is “the government’s policy on Brexit is disastrously damaging to the country and we would do something very similar”, the leadership could mount a credible opposition.

There is also a much more substantial case for Corbyn to raise the option of staying in the EU. Separately he is proposing a programme of radical change. Some of his policies address the concerns of those who have felt “left behind” in recent decades in much more practical ways than Brexit. But Brexit is sucking up the energies of Whitehall and will do so for decades.

There will be no space for a radical Corbyn agenda and Brexit simultaneously. Corbyn will never get the chance to implement his policies unless Brexit is halted. If it goes ahead on schedule in 2019, the current government will almost certainly stagger on until 2022, by which time Corbyn will have peaked. Equally pragmatically, Corbyn would reaffirm his rapport with younger pro-European voters while attracting those worried about the economic turmoil of Brexit. He would also kill off any moves towards the formation of a new party.

Can an opposition leader argue against the 2016 referendum outcome? Corbyn is better placed to do so than most. He can argue genuinely that he has had more doubts about the EU than many of those who voted for Brexit, but that the referendum was not an endorsement of the Tory Brexit deal that followed.

Has Corbyn always been a supporter of Brexit who would therefore never contemplate arguing that to remain is a better option? He shares with his hero, the late Tony Benn, deep concerns about the accountability of the EU and regards the way it has treated Greece as emblematic of much that is wrong with the institution. But I am told by close allies of Corbyn that the former Greek finance minister, Yanis Varoufakis, converted the Labour leader to the remain cause following a couple of long conversations ahead of the referendum.

Corbyn would do well to have another conversation with Varoufakis soon. Given the choice between the government’s Brexit deal, no deal and remain, it will be greatly in Corbyn’s interest to back remain.

• Steve Richards is a political commentator, broadcaster and author of The Rise of the Outsiders: How Mainstream Politics Lost Its Way