Is it possible to Boris-proof Brexit?

Politicians do not always keep their promises, and no one knows that better than a politician. It is little surprise, therefore, that Jeremy Corbyn’s Brexit team is trying to lock the government into whatever pledges No 10 makes on the Brexit deal. Corbyn is said to want to “Boris-proof” any cross-party agreement: if he cajoles May into commitments to a softer Brexit, including a customs union, then he does not want a harder Brexiteer unseating her and ripping it all up. Keir Starmer, Shadow Brexit Secretary, is reported to have told Labour MPs that any compromise agreement must be subject to a “Boris lock.”

Designing a Boris-proof Brexit will be a testing constitutional challenge. Merely shifting government policy would, of course, be nothing like enough. A new leader could simply shift it back.

Labour might, instead, demand that commitments to a customs union get written into the “political declaration,” the part of the Brexit deal that signals the direction of travel for the future relationship. This would be a moment of significant political theatre. The political declaration is, however, not binding or enforceable, so the practical impact of this step would be small. The withdrawal agreement itself is binding, but there is unlikely to be much mileage in trying to insert a permanent customs union there. The EU has said, again and again, that the withdrawal agreement is closed and cannot be reopened.

The vehicle for Boris-proofing any Brexit policy would probably, therefore, be legislation. If ever the government can secure a majority for a deal, it will bring forward a new “Withdrawal Agreement Bill” to implement the agreement in UK law. Labour could demand a clause in that bill which says that “it shall be a negotiating objective of the government to seek a customs union with the EU,” or similar.

That would be nothing like bulletproof. Though Labour may want the politics to follow the law, under the British constitution the law follows the politics. No Parliament can bind its successors. If Prime Minister Boris Johnson could rally a majority in the House of Commons to rip up the primary legislation directing his government to seek a customs union, then that would be the end of the matter. Even if today’s parliament tried some constitutional wizardry to make that harder—for instance, by requiring a majority of two thirds of MPs to change the negotiating objectives—it’s likely that 50 per cent of MPs plus one could always dodge that extra hurdle, by repealing the supermajority requirement itself. There is no such thing, in truth, as a Boris-proof Brexit.

Yet codifying the government’s negotiating objectives in law would not be entirely futile, for two reasons.

First, if a future government did want to change tack, it would be forced to confront parliament with its policy and build support for changing the law. That is exactly what the government has avoided doing throughout this process. Theresa May has always faced at least two ways.

She initially said that the UK would be outside any customs union with the EU, while proposing a “facilitated customs arrangement” that looked like a customs union in all but name. Now she tries to defend a deal which includes both a customs union (in the Northern Ireland “backstop”) and a commitment to leaving that customs union, trying to get Labour to focus on the former and her own party to focus on the latter. Everyone is confused and no one is satisfied. If her successor were forced to defend and explain the government’s policy, rather than obscuring it with tangled doublespeak, then that would be no bad thing.

Second, if the government ends up sticking to the negotiating objectives rather than trying to ditch them, then it will be handy to have won parliament’s approval for the thrust of its policy once already. Inevitably, ministers will have to return to the Commons seeking approval for any future relationship treaty. If a majority of MPs get behind a customs union (or whatever else) in the next few weeks, then they will have dipped their hands in the blood. Having willed the ends, they will need a good answer to the question: why oppose the means?