Image source, PA

Mrs May is reportedly meeting Sir Graham Brady, the chairman of the influential 1922 Committee of Conservative backbench MPs.

Also known as "the 22", the group meets weekly when the Commons is sitting.

Sir Graham, representing these backbenchers, is the person who Conservative MPs must write letters to when they call for a vote of no confidence in the prime minister.

At the end of last year, Sir Graham received 48 letters - the threshold needed - to hold a no confidence vote in the PM, which she survived.

Under current party rules, there can't be another vote for a further year so the PM is technically safe until 12 December this year. Many MPs want to change the rules to allow an earlier contest - but this would need to be agreed by the 1922 Committee.

Image source, PA

Confirmed candidates:

• International Development Secretary Rory Stewart
• Former Leader of the House Andrea Leadsom
• Former Work and Pensions Secretary Esther McVey
• Former Foreign Secretary Boris Johnson

Possible candidates:

• Steve Baker
• Brexit Secretary Stephen Barclay
• Chair of the 1922 Committee Graham Brady
• Environment Secretary Michael Gove
• Health Secretary Matt Hancock
• Mark Harper
• Foreign Secretary Jeremy Hunt
• Home Secretary Sajid Javid
• Housing Minister Kit Malthouse
• Defence Secretary Penny Mordaunt
• Work and Pensions Secretary Amber Rudd
• Former Brexit Secretary Dominic Raab

• Chief Secretary to the Treasury Liz Truss

As Jessica Parker explains, there are quite a few who fancy their chances...

Norman Smith
Assistant political editor

There was a move to oust Theresa May in December – that failed.

Under the rules, that means they can't have another crack at it for a year, so she was safe until December.

However given the unfolding car crash of the Brexit negotiations there was clearly an appetite to oust Mrs May.

So the 1922 committee was looking at rewriting or suspending the rules.

On Tuesday night they had a vote to suspend the rules and from those I have spoken to it is clear that there was a majority for suspending the rules.

So when Sir Graham Brady is talking to the PM he does have a letter with that rule suspension in his pocket - in case she says she is hanging on.

It's a sunny morning in central London today, and the media is waiting in Downing Street to follow the action.

Image source, Reuters

Image source, Getty Images

Norman Smith
Assistant political editor

I'm not sure what political point she [Helen Grant] is trying to make by resigning.

Mrs May is going. I can't honestly say it seems to be a game-changer.

Theresa May arrived back in Downing Street with her husband, Philip, this morning.

Image source, Getty Images

In her resignation letter, Helen Grant says she has resigned the role because she wants to "actively and openly support one of the new leadership candidates".

Norman Smith
Assistant political editor

The reality is that Theresa May's Brexit deal is dead and her fate is tied to that.

Yesterday there were clear signs she wanted to fight on.

But the reality seems overwhelming. There was the backlash from MPs to her Brexit deal and then, yesterday, Jeremy Hunt and Sajid Javid told her: "you really can't get this through."

And now there is the meeting with Sir Graham Brady.

They will be encouraging her to leave of her own volition rather than being dragged out kicking and screaming.

And I think that is the conclusion she is reaching.

Rob Watson
BBC political correspondent

Theresa May's time as prime minister is drawing to a close.

The precise timing and choreography of leaving are not yet clear, but should become so in the next few hours.

Her legacy is uncertainty over Brexit and a party and country even more divided than when she first entered No 10.

Up next - a likely ugly and bruising battle to succeed her as Conservative Party leader and prime minister.

And no obvious route ahead for whoever succeeds her to solve Brexit and reunite the country.

The prime minister's resignation would kick off a Conservative Party leadership contest.

The 1922 committee decides the conduct of the election in consultation with the party board – including the timetable.

If it starts on 10 Jun, as speculated, and runs to the "normal" length it would go beyond the end of the parliamentary term so they will have to speed things up a bit to get it done by the summer break.

Normally there would be time for candidates to come forward - then the whittling down to two through sequential votes of Conservative MPs.

In the past these have been on Tuesdays and Thursdays, so only two a week.

Then ballot papers have to be sent out to members and returned by post after a period of campaigning (potentially involving hustings).

Welcome to our live political coverage amid reports from ministers that Theresa May could announce her resignation today.

Mrs May is under pressure to quit after a backlash from her own MPs against her Brexit plan, which has been rejected three times.