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

Welcome to The Independent's politics liveblog, where we will be bringing you all the latest updates from Westminster throughout the day.

Here is today's front page, with our splash on talks about Labour's Brexit stance among the party's affiliated unions. You can read the full story here.

MPs are poised for a day of drama in the Commons today, as there is a piece of actual legislation on the order paper.

After weeks of drift, the government has been forced to bring forward the Northern Ireland (Executive Formation) bill to delay the deadline for the formation of the Stormont Assembly. 

Tory Brexit rebel Dominic Grieve seized on the chance to try to amend the bill, to force the Commons to sit right up the 31 October Brexit deadline. If it wins - and it might - then a new PM would be prevented from forcing through a no-deal Brexit.

More here:

Tory former leader Lord Hague has told Boris Johnson to rule out suspending parliament to try to get a no-deal Brexit through if he becomes prime minister.

Lord Hague told BBC Radio 4's Today programme: "It is very important that parliament is able to give its opinion.

"It ought to be unthinkable that we could leave the European Union by a manoeuvre, by a procedural ruse of some kind."

Asked if Mr Johnson should rule out proroguing parliament to get a no-deal Brexit, Lord Hague said: "He should rule it out. Yes."

Another day of fallout on the sensational leak of diplomatic cables from UK ambassador to the US, Sir Kim Darroch, calling his administration “dysfunctional” and “inept”.

In an outburst remarkable even by his standards, Donald Trump said on Twitter the US would no longer deal with Sir Kim Darroch, who has served as British ambassador to Washington since January 2016. 

Read the story here:

The culprit behind the leak of sensitive diplomatic messages was intent on sabotaging the British ambassador to the US in order for them to be replaced by someone "more congenial", a former ambassador has said.

Sir Christopher Meyer said there was a "possible range of villains" who could be responsible for the leaking of memos in which Sir Kim Darroch described the US administration under Donald Trump as "inept".

He told the Today programme: "Here there is a possible range of villains who come into the frame.

"But it was clearly somebody who set out, deliberately, to sabotage Sir Kim's ambassadorship, to make his position untenable, and to have him replaced by somebody more congenial to the leaker."

Tory former foreign secretary Lord Hague also condemned the leak.

He said: "You can't change an ambassador at the demand of a host country.

"It is their job to give an honest assessment of what is happening in that country."

Justine Greening today tells Cabinet ministers opposed to a no-deal Brexit to stop “sitting on their hands” and to find the strength to stop it, with time running out fast.

The former education secretary lashes out at colleagues – including ministers – who she said “talk tough” but who have “spent the past year saying now is not the right time to act”.

“It’s like standing by whilst a car crash happens and then expecting thanks for arriving with a first aid bag too late,” Ms Greening protests, in an article for The Independent.

Boris Johnson and Jeremy Hunt will appear on a live ITV debate at 8pm, which could help to decide the outcome of the contest.

Mr Johnson will hope to use the occasion to further reinforce his lead while Mr Hunt will have a final chance to turn around a contest in which he has been the underdog throughout.

There has been frustration in the Hunt camp at the reluctance of his rival to engage in direct debate.

Although both men have taken part in numerous hustings - where they take questions separately from party members - Mr Johnson has agreed to take part in only one previous TV debate, when there were still five contenders left in the race.

Ballot papers started going out last week to the party's estimated 180,000 members, and many will already have voted, meaning that the potential for the debate to alter the course of the contest may be limited.

Philip Hammond is calling for Conservative MPs to be handed a free votein tonight’s Commons clash to prevent a no-deal Brexit, a move that would hugely boost the chances of success.

The chancellor is understood to be pressing Theresa May to make the key concession, as part of negotiations on the prime minister’s hopes for a cash boost for education before she leaves No 10.

The free vote would be granted on any amendments to stop Boris Johnson – the near-certain next prime minister – suspending parliament to carry out a crash-out Brexit on 31 October.

A massive inquiry is under way in Whitehall for the source of revelations which threaten to undermine UK diplomacy, writes political editor Andrew Woodcock.

Who is the leaker?