On Wednesday at 1.30pm, Labour’s shadow cabinet, in a special Brexit session, may move towards making the historic decision to call for a referendum for “all circumstances” - that is on any Brexit deal agreed by parliament or on a no-deal Brexit.

That said, sources close to Jeremy Corbyn caution me against expecting any momentous announcement.

By contrast, shadow cabinet members tell me that Corbyn is inexorably - if slowly - shifting Labour to become the referendum party, although one senior party member tells me a device will be found to delay the shift.

What gives credence to the idea that there will be a decisive move towards a confirmatory ballot is that Andrew Fisher - Corbyn’s policy adviser - has written a paper recommending that.

And - more surprisingly perhaps - he is also said to have recommended that Labour should simultaneously adopt a position of campaigning to remain in the EU.

I am told that Corbyn’s closest advisers - Seamus Milne and Karie Murphy - will swallow the referendum (which they have always resisted) but want to keep open the idea that a Labour government could negotiate a superior and acceptable Brexit.

Keir Starmer (left) is thought to favour a second referendum. Credit: PA

A source told me: “Papers are written all the time; they are not official policy”.

There will certainly be a lively discussion at Wednesday's shadow cabinet on whether Labour should full-throatedly become the referendum-and-remain party - with Starmer and Watson enthusiastically backing that shift and Lavery and Trickett still resisting.

As I said, most Labour MPs think it is simply a matter of time before Labour becomes the referendum party, because even in leave-voting constituencies they say their members and supporters increasingly want that.

But many worry that this significant movement away from supporting Brexit will come too late to reverse the significant increase in popularity of the Liberal Democrats or to mount an effective campaign of persuasion in leave-leaning seats.