Only a few years ago, the notion of Jeremy Corbyn citing the CBI and the Institute of Directors against a Conservative prime minister would have appeared absurd. But on the issue of Brexit, Corbyn is now able to boast that it is Labour, not the Tories, who are the pro-business party.

The opposition's embrace of a customs union with the EU has given Corbyn the dividing line he needs. At today's PMQs, he relished in the Conservatives' divisions, as Tony Blair did during the dying days of the Major administration. “This is a government in disarray,” Corbyn declared. “Every time the cabinet meets all we get is ever more bizarre soundbites.”

If this was one of the Labour leader's strongest performances it was partly because he had no shortage of ammunition. Corbyn ridiculed Theresa May's opaque proposal of “ambitious managed divergence” (“Could she tell the country what on earth it would mean in practice?”) and he seized on Boris Johnson's leaked letter to May stating that “it is wrong to see the task as maintaining ‘no [Irish] border’”.

Though May protested, as ever, that she and Johnson were “absolutely committed to ensuring that we deliver on no hard border between Ireland and Northern Ireland”, her words grow less credible by the day. (Labour MPs shouted “coward!” at Johnson as he skulked out of the chamber before an Urgent Question on the Irish border).

By exploiting the cabinet's unbridgeable divides, the Labour leader showed that he has travelled a long way since he dismissed the need to mock Iain Duncan Smith's resignation in 2016.

Corbyn, who the Tories have repeatedly declared a threat to prosperty, was also able to note that 94 per cent of small and medium-sized businesses believed the government was ignoring their concerns. Who, he asked, knows best: business or Trade Secretary Liam Fox? Again, like Blair in the 1990s, Corbyn is colonising traditional Tory territory.

May, trapped between the demands of her party and those of the EU, had no memorable or original riposte. And no longer can she accuse Labour of indecision. When May charged Corbyn with seeking to “betray the vote of the British people”, the charge failed to resonate. Corbyn has made it clearer than ever that he has no intention of overturning the referendum result (not least due to his lifelong Euroscepticism). And few believe that the public voted Leave for the right for Britain to strike its own (unfavourable) trade deals (polls, for what it's worth, show that voters support a customs union).

For too long, Brexit has been a political weakness for Labour. Today, Corbyn turned it into a strength.