MPs opposed to a no-deal Brexit will make an almost-final attempt early this coming week to make it impossible for - if he becomes PM - to prorogue or suspend parliament to force through a no-deal Brexit.
The plan which has been designed largely by , the senior Tory MP and former attorney general, would amend the Northern Ireland (Executive Formation bill) - which is due to be debated on Monday - to force the government in October to make an oral statement on the progress of efforts to restore fully devolved government to Northern Ireland.
If the amendment were to pass, it would mean the House of Commons would have to sit in October.
It would therefore be impossible for the new prime minister to prorogue parliament or send MPs home in the days before the October 31 official date that the UK is scheduled to leave the EU.
So if the amendment is accepted, it would give MPs who hate a no-deal Brexit an opportunity in October to pass a law that would bind the new PM to leave the only EU with a deal - which would in theory make a no-deal Brexit impossible.
The amendment is bound to be supported by Labour, and a number of Tory MPs, such as Ken Clarke, Antoinette Sandbach, Justine Greening, Caroline Spelman and Sir Oliver Letwin.
But the big question is whether it would be supported by cabinet minister vehemently opposed to a no-deal Brexit, such as the Chancellor Philip Hammond, the work and pensions secretary Amber Rudd, the justice secretary David Gauke and the business secretary Greg Clark.
Theresa May is expected to order her MPs to oppose the amendment by enforcing a so-called three-line whip.
All Tory MPs have been ordered to cancel engagements and be in parliament on Monday and Tuesday.
But one MP told me the three-line whip ought "to have no impact on Rudd, Hammond, Gauke and the others" because "everyone knows Boris will sack them in a fortnight so they will have nothing to lose any longer".
Also, Johnson’s rival to be Tory leader and PM, Jeremy Hunt, is on record as opposing a prorogation of parliament to force through a no-deal Brexit, so the foreign secretary too should back the amendment.
A source close to Hunt told me he had not made up his mind what to do.
I understand this will be the last attempt by Tory MPs before the summer recess in late July to make a no-deal Brexit a more remote prospect, although if they lose this week they will try to restart their offensive in September.
There are also like to be other hotly debated amendments to the Northern Ireland bill, to force the province to legalise abortion and recognise gay marriage.
These amendments will split the Tory Party because they are opposed by Northern Ireland’s DUP - whose 10 MPs prop up the government.
One senior Tory said her female colleagues were likely to support the legalisation of abortion and gay marriage whereas many men world abstain.
"The men are pathetic" said the source.