By THE EDITORS / Pic By BLOOMBERG

THE deal that UK Prime Minister Boris Johnson has just negotiated with the European Union (EU) isn’t the worst conceivable outcome to the long saga of Brexit.

Unfortunately, that’s about the best one can say for it.

Johnson had vowed to improve on the exit agreement secured by Theresa May and arguably he has succeeded in some respects. His deal replaces the hated UK-wide “backstop” that May agreed to with one that applies only to Northern Ireland; leaves Northern Ireland aligned with the EU’s single market; imposes a customs boundary in the Irish Sea, thereby avoiding a hard border with Ireland; and creates a complicated system for lawmakers to eventually opt out of the arrangement.

This approach resolves or elides some of the dilemmas that led the Parliament to reject May’s deal three times over. And it’s surely better than a chaotic and costly no-deal exit. Even so, it’s nothing to celebrate.

By ditching the customs union and abandoning May’s commitment to a close trading relationship in goods, it will wrench Britain further away from the EU and impose more costs and barriers. By one estimate, Britain’s per-capita GDP could be reduced by over 6% over 10 years, only slightly better than leaving with no deal at all.

The rationale for this approach is that the UK will be able to conclude its own free-trade deals around the world. There are reasons for skepticism.

Of the 40 or so deals the EU has in place, Britain has so far managed to “roll over” just 15. And by the government’s own reckoning, additional deals would probably add only about 0.7% to GDP over the long term.

More ominously, Johnson’s deal could place further strain on Britain’s union. Scotland may demand similar treatment to Northern Ireland or once again pursue independence.

The logic of a united Ireland may become more compelling as Great Britain and Northern Ireland diverge. Even many Welsh now say that independence would be preferable to leaving the EU, a sentiment that could intensify as the UK becomes less competitive.

With the Brexit deadline of Oct 31 bearing down, the Parliament considers the deal. Its prospects are tenuous. The Democratic Unionist Party, which props up Johnson’s ostensible majority, has already rejected it.

Brexit hardliners may yet find it insufficient. And Johnson will have to plead for votes from quite a few Tories whom he recently expelled from the party. The best path forward would be for lawmakers to demand that this deal, if it passes, be ratified by a second referendum.

That would confer some measure of democratic legitimacy on a bargain that looks very different from what Brexit campaigners originally promised. It would give voters an informed choice now that the costs and benefits of leaving are clearer. And it would make the deal more sustainable as Britain and the EU prepare for many months of grueling talks over their future relationship.

Not least, it would also offer voters a final chance to do the right thing and reverse this calamitous process. Johnson’s deal may have avoided the worst. But the one thing it cannot paper over is that Brexit remains a terrible idea. — Bloomberg

This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.