Tory leadership debate – live: Johnson refuses to say whether he would resign if Brexit deadline is missed as he flounders over US diplomatic row

Today is also shaping up to be a busy day for Labour.

The shadow cabinet is meeting to discuss the unions' joint statement on Brexit, with some words from Jeremy Corbyn expected later today. 

Labour's ruling body - the national executive committee (NEC) - is meeting today too, where the disputes committee will also discuss Chris Williamson's case. The Labour MP was suspended over allegations of antisemitism.

Things look heated outside Labour HQ.

Another issue dominating in Labour circles is the looming prospect of deselections.

Sitting MPs had until Monday to declare whether they would stand again for the party, with six MPs deciding that they will bow out at the next election.

Brexiteer Kate Hoey, who lost a confidence vote of Vauxhall members last year, has said she will not stand, while Stephen Pound, Stephen Twigg, Jim Fitzpatrick, Kevin Barron and Ronnie Campbell have declared they intend to step aside for various reasons.

It comes after a change in party rules, which lowered the threshold for a so-called trigger ballots, making it easier for members to deselect their sitting MP this year. 

According to party documents, an MP will face a trigger ballot if "one third or more of Labour Party branches or one third or more of affiliated branches, who return their ballot, indicate they wish a selection to take place".

The MP will then face a contest with other party members over whether they are selected to fight the seat.

Jeremy Corbyn has written to members, saying Labour would campaign for Remain against a no-deal Brexit or a "Tory deal".

He says: "Whoever becomes the new Prime Minister should have the confidence to put their deal, or No Deal, back to the people in a public vote.

"In those circumstances, I want to make it clear that Labour would campaign for Remain against either No Deal or a Tory deal that does not protect the economy and jobs."

Lots of chatter amongst journalists about what that Jeremy Corbyn email really means.

Jeremy Corbyn has challenged the next Tory prime minister to put their Brexit deal to a referendum and announced Labour will campaign for Remain in such a public vote.

Read our developing story here:

Meanwhile, a government insider has accused Downing Street of allowing the creation of “elephant traps” for the next prime minister on Brexit.

The accusation came as MPs prepared to vote on an amendment tabled by former attorney general Dominic Grieve which would effectively block Tory leadership frontrunner Boris Johnson from suspending parliament to force a no-deal Brexit through.

The insider said that Number 10 could have stopped the vote - along with a failed cross-party attempt last month to seize control of the parliamentary agenda in order to prevent no deal on 31 October - if its focus was fully on giving Theresa May's successor the best chance of delivering Brexit.

There are no urgent questions or statements, so we expect the Northern Ireland bill around 12.45pm. John Bercow, the Speaker, will announce which amendments he has chosen before it begins. 

NEW - the Dominic Grieve amendment is not selected by the Speaker, so MPs will miss out on their chance to block a no-deal Brexit today. 

Mr Grieve's new clause 14 had sought to keep government in Northern Ireland running in the absence of the devolved institutions, requiring parliament to come back to the issue in October.

The move was designed to try to ensure the next prime minister cannot push through a no-deal on October 31, the current EU deadline for agreeing on a deal, simply by suspending, or "proroguing", Parliament.

But it was not included in a list of amendments to be considered at committee.

Mr Bercow has selected, among others, new clause one - a cross-party proposal, led by Labour's Conor McGinn, to require Westminster to legalise same-sex marriage in Northern Ireland if a new Stormont Executive is not formed by October 21 2019.

Theresa May has told ministers it was "absolutely right" that they continued to give their full support to the UK ambassador to the US, Sir Kim Darroch.

The PM told cabinet that leaked memos in which Sir Kim sharply criticised the Trump administration did not reflect the closeness of the relationship with the US.

After Mr Trump said the administration would no longer deal with Sir Kim, Mrs May stressed it was important ambassadors were able to give "honest and unvarnished" assessments to ministers.

"She said it is absolutely right that we continue to give Sir Kim Darroch our full support," the PM's official spokesman said.

"The ambassador remains in post and continues to carry out his duties with full support of the PM."

John Bercow has made a statement in the Commons just now about the amendment selection for the Northern Ireland bill. He says his office received a call from a “tabloid scribbler” last night who had heard the Speaker would not be chairing the proceedings this afternoon.

He says it is a long-established convention that the Speaker does not chair proceedings for a committee of the whole house - one of his deputies does - which goes back to the 17th century.