Since the summer, Downing Street’s political strategy has been clear. It has systematically talked up the prospect of no deal in the hope that any deal will be judged a success in comparison. That’s why the government has published a steady flow of technical papers on Britain’s preparedness: from chartering ships to bring in food supplies to stockpiling medicines to advising businesses to simply leave the country. The anxiety levels of parliamentarians and the public has understandably risen. Perhaps that was the point all along.

Yet no deal has always been the least likely outcome. Setting aside the consequences for the UK, a no-deal Brexit would mean that pan-European overnight bank clearing could not take place, causing the global financial system to crash for the second time in a decade. With 48% of European aviation insured through London, half the continent’s planes would be grounded. Nearly 80% of Europe’s capital markets are in London and might be inaccessible.

In the 21st century, no British prime minister is going to let one of the world’s most advanced nations struggle for food and medicine. And even if Theresa May were prepared to follow through on her threat, parliament – where perhaps 600 of 650 members oppose no deal – would never allow her to do so. So no deal is simply a hoax, an act of political deception. So far, it’s working.

The right response from remainers would have been to call out the government and focus on the quality of the deal rather than the plausibility of achieving one. Leavers made big promises in the referendum, and it is right that they should be held accountable. And yet rather than offering sober analysis, many remainers appear drawn to the doomsday scenario, as if confirming their worst suspicions is what matters most. So they have become accidental collaborators, amplifying precisely the message the government wished to get through.

The endless speculation about a potentially disastrous outcome has occluded serious assessment of what is desirable. Virtually all economists agree that no matter what deal is struck, leaving the EU will damage the UK economy. While the sky will not fall in, different arrangements have very different economic impacts. It is therefore the responsibility of every parliamentarian to make the best assessment of whether the government’s eventual proposal is in our national interest or not – whether it protects or advances our interests, not merely whether it averts disaster.

The government is set to ask parliament and the country to take a leap in the dark and vote for a “blank Brexit”. Britain and the EU will have a legally binding agreement for the withdrawal and transition, but a political declaration for the future partnership. Crucially, the political declaration will have no legal force. Brexit protagonists will have everything to play for from April next year. The cliff edge so feared by business will have been postponed for 21 months, but not eliminated.

The prime minister may declare “prosperity in our time” but as Neville Chamberlain found at Munich, a political declaration is little more than a scrap of paper. The UK will have traded its most significant negotiating card – the financial settlement of nearly £40bn – for the standstill transition. Forget £350m a week for the NHS, it will mean the transition has been bought for £2bn a month. We will have lost the ability to change our minds and withdraw article 50 notification. And by insisting on a time-limited transition – rather than a formulation such as “as short as possible, as long as necessary” – we will not be able to play for time.

Moreover, the single market is much more important to us than the UK market is to any of the 27 remaining member states. While the single market accounts for nearly 50% of total UK trade in goods and services, the UK accounts for less than 8% of total trade for most individual EU states. If Britain leaves the EU on this basis, we will be left extraordinarily exposed, reliant on the kindness of strangers to secure a good deal. This leap in the dark is a huge gamble for the country to take.

It is precisely this asymmetry in negotiating leverage that will mean European leaders will join the government in calling on MPs to vote for its proposal. They have every incentive to send the UK into purgatory and so will claim the alternative is no deal. With such a chaotic and divided approach to negotiations from the UK, it should be little surprise that the EU will recommend that British parliamentarians pass the vote. It will reflect the fact that they have negotiated far more successfully, securing their interests rather than ours.

Despite these clear disadvantages, do not be surprised if the business lobby gears up to support the government’s plan. The extremism of the Brexit ultras has played into the government’s hands and much of the business community now seriously believes that swathes of the Conservative party would positively welcome the UK crashing out of the EU.

But politicians from all parties need to hold their nerve. It is their duty to critically examine the government’s proposal to determine whether it is in Britain’s long-term national interest. Neither the British public nor history will reflect kindly on those who sacrificed the right deal for any deal. MPs representing leave-supporting constituencies may fear the electoral consequences of voting against the government’s plan, and vice versa, yet with the next general election likely to be in 2022, voters will be less interested in how their representatives choose to vote now than whether they have a good job and rising living standards in years to come. If there is a good outcome, and the economy does reasonably, then the government will get the credit. If there is a bad outcome, and the economy suffers, voters will hold both those who promoted Brexit, and those who enabled it, to account.

• Tom Kibasi is director of the Institute for Public Policy Research and founder of the IPPR Commission on Economic Justice. He writes in a personal capacity