Theresa May has finally realised she desperately needs Labour's backing on Brexit – here's how she could secure it

The prime minister opposes a permanent customs union for now, but it is her best option – even though it would scupper trade deals with non-EU countries

Theresa May’s appeal to Labour backbenchers and trade union leaders to rescue her unloved Brexit deal is desperate, very late in the day and long overdue.

She could and should have already built a cross-party alliance for a soft Brexit – either in 2016 when she became prime minister (to represent the 48 per cent, instead of treating the 52 per cent as if they were 100 per cent) or after the 2017 election (to recognise the parliamentary arithmetic against a hard Brexit that has now belatedly dawned on her).

Moderate, pro-European Tory MPs have been urging May for months to reach out to Labour MPs. She ignored them. So they formed their own alliances with their Labour counterparts. The result: the government’s two Commons defeats on Brexit this week, with more to come. There is a cross-party network but May is not yet part of it.

May consistently told her aides she wanted to get a Brexit deal through with Tory and DUP votes. Like Jeremy Corbyn, she is a tribal animal. Hardline Eurosceptics repeatedly warned her not to cosy up to the Labour enemy. Understandably, May didn’t want her party to split on her watch – one Brexit scenario. Etched firmly in Tory minds are the party’s breakup over the repeal of the Corn Laws in 1846 and its divisions over tariff reform in 1906. Both cost it power.

With hardline Brexiteers and the DUP set to inflict a heavy defeat on May in next Tuesday’s Commons vote on her deal, she had to try a different track. But is her appeal to Labour MPs too little, too late?

I doubt that more than a few of them will support her next week. Those who have met May want more carrots – for example, a firm commitment to maintain EU levels of regional aid in their patches. However, they might back a revised version of her deal in a second or third Commons vote, in order to head off a damaging no-deal Brexit on 29 March.

May’s problem is that even then, she might win the support or abstention of only 20-30 Labour MPs – not enough to counteract the Tory-DUP rebellion. To win significant Labour backing, she would need to make a permanent customs union her plan B. Although she opposes it for now, it is an option. But it would scupper trade deals with non-EU countries. If the Commons coalesced around Norway Plus, inside the single market and a customs union, May would also have to swallow free movement.

Some ministers float the customs union idea. But I wonder whether this, and May’s attempt to woo Labour MPs, is partly a ruse designed to bring some of her 100-plus Tory critics back onside. Their numbers are much bigger than potential Labour backers. Seeing May’s direction of travel, some Tories might grudgingly conclude that her deal is better than further concessions to Labour. May can’t afford to give up on her own side. Significantly, Jeremy Hunt, the foreign secretary, played up the threat of “no Brexit” on BBC Radio’s Today programme on Friday morning and, acknowledging the Commons mood, played down the prospects of the no-deal Brexit some Eurosceptics favour.

A permanent customs union is Labour’s policy. But I doubt Corbyn would ride to May’s rescue if she embraced it, despite the olive branch he offered her at last autumn’s Labour conference.

Corbyn wants a general election, which means shooting down May’s deal in whatever form it takes. A more intriguing question is whether the Labour leadership allows its MPs a free vote when the Commons starts to discuss a possible plan B.

Nor is it impossible that May ends up offering free votes. It would show she is serious about building a consensus. There is a precedent: in 1971, when the UK voted to join the European Economic Community, the Tory prime minister Edward Heath did not whip his MPs. That encouraged 69 Labour MPs to rebel and back entry, wiping out a revolt by Eurosceptics.

The other important player in next week’s drama will be the EU. I suspect its response to May’s defeat will be surprisingly helpful to her. The reassurances on the Irish backstop it offers before Tuesday’s vote will not be its last or most important word. The EU will have other cards to play to avoid the no-deal scenario it does not want. “We need to see what the Commons will accept first,” one Brussels insider told me. That is why the EU was so exasperated when May postponed the crunch vote last month.

So May still has a fighting chance of eventually getting a revised version of her deal through. But she will have to reach out way beyond her comfort zone, match her conciliatory words with deeds and make real compromises. She will probably have to extend the Article 50 process beyond March. None of this will come naturally to our stubborn prime minister. Is she capable of it? We’ll soon know.