A second referendum during Brexit negotiations would be absurd

An eerie truth is starting to dawn. Theresa May and Jeremy Corbyn agree on Brexit. They are both realists. They know Britain needs a customs union with the EU. Perhaps they should go off to a Welsh mountain together, and do a Trump/Putin? Either way, it is time for parliament to offer united support to Britain’s negotiators in Brussels, as it did to the leave decision on article 50.

On Sunday, May’s former education secretary, Justine Greening, added to her misery by calling her Chequers negotiating compromise a fudge. All compromises are that. In truth Chequers was a tactical way-station to the inevitable: a customs union. It was not ideal, but it was progress, and anything else is fantasy. Greening complains May’s union would leave Britain with “no say on shaping” EU trade rules. But that is what leave meant. In reality, Norway, the US, even China, have plenty of say on trade rules with the EU where it affects them. Trade on goods with the EU is a trivial aspect of Brexit.

Greening, a desperate remainer, joined calls for a second referendum on Brexit, though on the BBC’s Today programme she confused a referendum on “the Chequers deal”, which she calls unworkable, with a referendum on “the final negotiated deal”, which is as yet unknown. The idea of asking the electorate its opinion during a negotiation is absurd. The constitutional position is clear. The vote was “to leave the EU”. It is for parliament and those negotiating on its behalf to decide how.

According to Greening, parliament is in stalemate over Brexit, yet there is wide parliamentary support for customs union. The jam is party political. This week promises more chaos over amendments to the Brexit bill, but out of it must come a “coalition of sanity” in favour of customs union. Britain’s negotiators in Brussels cannot go on talking when the other side knows they have a divided political community behind them.

The reality is that the argument over a customs union is a distraction, largely because it has allowed the hard Brexiters to talk about “making our own trade deals”, when this is pie in the sky. Every poll of leave voters shows them uninterested in trade barriers with Europe. What they wanted, and still want, is a degree of immigration control. This wholly separate issue is hotly debated across Europe at present, and can at least be put on hold.

When this process is over and Britain has embarked on a transitional period of leaving the EU, it might indeed be sensible, as in 1975, to heal the bruised body politic with a second referendum. The mind boggles at the consequence of it being lost. More plausible would be for parliament to agree to seek a fresh electoral mandate for the leadership of post-Brexit Britain. Then I suspect we shall wonder what all the fuss was about.

• Simon Jenkins is a Guardian columnist