Cabinet ministers meeting today to discuss our membership of a European customs union hold the fate of two achievements in their hands.

The first is Britain’s global renown as a beacon of free trade; the second is the Conservative Party’s re-won reputation for economic competence.

The first matters for millions whose livelihoods depend on our future as an open economy.

The second matters for Tory MPs staring at defeat if they offer the electorate an economic plan driven by ideology, much like the programme offered by Jeremy Corbyn.

The facts are these. Britain’s membership of a European customs union means goods manufactured here can move freely into our nearest and largest export markets without having to pay tariffs or comply with bureaucratic rules of origin.

There is nothing unique to the EU about such arrangements. Customs unions exist in Latin America and the Gulf without loss of sovereignty.

Nor is membership of a customs union the same as membership of the EU, as some claim. Turkey is an example.

From their emergence in the 19th century, customs unions have been rightly seen as progressive acts of free trade.

The converse is true. If Britain is no longer part of a customs union, there will be “unavoidable barriers to trade” however clever the border technology, as Michel Barnier says.

There is no escaping the simple economic truth: outside of a customs union, the cost of the things we buy will go up.

The opportunities for British firms to sell abroad will be reduced.

Britain will have consciously engaged in the biggest act of protectionism in our history.

Economic logic

Who wants us to embark on such a destructive path?

Not British business — the overwhelming majority of which want to remain in a customs union.

Not our Irish neighbours — a customs union is the only sure way to preserve an open border on the island.

What about those who want Britain to export more? The Government’s analysis is telling: leaving a European customs union would cost us several percentage points of GDP (trillions of pounds); whereas new trade deals with the US and others could add only 0.6pc of GDP back.

It doesn’t add up; nor does that oft-repeated Brexiteer claim that customs union membership prevents us doing more trade with the fastest-growing parts of the world. Where’s the evidence?

Germany exports five times as much as we do to China. None of the services deals advanced by the Prime Minister in Beijing last week are inhibited by customs union membership.

Yes, outside a customs union we could let in products that are currently banned or subject to quotas. Let the Brexiteers spell this out.

It is hard to believe that the 17 million people who voted to leave the EU in places such as Sunderland, Port Talbot and North Yorkshire did so to allow in more Chinese steel and American chlorinated chicken sales.

Economic logic suggests we should remain in a customs union. We know that it is what the great majority of the Cabinet privately believe.

There are growing signs that it is what a majority in Parliament want, and will vote to impose. So who objects?

A handful of ultra-Brexiteers, caught up in the perverse logic of their misguided revolution.

Any damage to business, any restriction to trade, any cost to consumers, is worth it for the purity of saying: we will have nothing whatsoever to do with Europe.

Why do the views of these zealots have any hold on the country’s future? Because the Conservative leadership appears to be too weak to resist.

A party famed for pragmatism has been held hostage by ideologues. A country renowned for its free trade risks becoming a force for protection.

For 19 months the Cabinet has ducked a choice which now has to be made.

If it won’t lead in the national interest, it’s time for Parliament to take back control.