Bernard Jenkin’s warning to Theresa May is that she can only carry a parliamentary majority if she sticks to the current plan for Brexit – and that means leaving both the single market and customs union.

The MP is right: the Brexiters do have the numbers, but only in one sense. There are comfortably more ardent campaigners for leaving the EU on the Tory benches than the 48 politicians required to force a leadership contest, and in doing so topple the prime minister.



And yet, on the wider parliamentary mathematics, I suspect Jenkin is wrong. If there is a Brexit majority in the House of Commons it is for a soft agreement with the EU, certainly including some form of customs union with the bloc, and perhaps even with enough votes for remaining within the single market.

After all, we know this is the position largely supported by opposition parties apart from the handful of DUP MPs.

Labour is a bit mixed but ultimately wants to replicate the economic benefits of both groupings, accepting there is a price on free movement and other issues to secure that. There is also a vocal group of Tory remainers firmly on side.

But more than that there is a much larger group of Conservative politicians who are loyal to the prime minister but privately back the desire of both the chancellor, Philip Hammond, and the home secretary, Amber Rudd, to retain as close as possible the economic relationship with the European Union.



For now, all those politicians (including Hammond and Rudd) are fully behind May’s commitment to a bespoke and ambitious trade deal that delivers all the economic benefits of the single market and customs union, without meeting all the obligations.

But as one senior Tory official admitted to me, the stated government position is a bit of a “having your cake and eating it option”.



If May achieves that, she’ll clearly command the support of the House of Commons. But if, in the end, MPs are faced with a choice between an Efta-style deal (similar to Norway) or a more basic Canada-style free trade agreement (even with some additional element of services added on) then the majority would be likely to tip towards the former.

And that is May’s catch-22, which starts to explain the latest debate over the customs union.

The Brexiters, perhaps because they ultimately don’t believe the cake model will play out, think that in recent weeks they have smelled a rat – for a number of reasons.



First, they are furious at Hammond’s suggestion, at a speech to the CBI in Davos, that the UK and EU economies would move only “very modestly apart” after Brexit (although to be fair to the chancellor, that is what the government’s position seeks to achieve, just without too much of a cost attached).

Second they believe that Treasury officials are convinced that Britain should stay in a customs union and think they were coming close to persuading the prime minister of that position.

And finally they are deeply suspicious of a line in government legislation being drawn up on a post-Brexit trading relationship that leaves open the possibility of creating a customs union.

That is enough for the Brexiters to start banging their drums – and loudly, to remind May of their leverage; not a parliamentary majority as Jenkin suggested but a Conservative caucus big enough to cause major problems.



Which is why May was quick to state and restate her government red line – that whatever the outcome of talks, Britain must be able to strike trade deals with third parties (for both goods and services) after Brexit.



All of which creates an awful lot of background noise as the prime minister and David Davis sit down with Michel Barnier on Monday ahead of the next round of talks. Not that the customs union (or a customs union or even a customs partnership) after leaving the EU is on the agenda. First Britain and the European commission are thrashing out the terms of a transition period.



And on that – perhaps in another concession to the all-powerful backbench Brexiters – a row is likely to focus on the question of EU citizens’ rights and whether they change in March 2019, or two years later at the end of transition.

Already causing a backlash in Brussels, this underlines the complexities about to be faced by British negotiators in the next phase of talks.

And that’s before they even embark on the future trading position.

