Theresa May
Theresa May is on the brink of a leadership challenge with multiple sources suggesting over 48 Conservative MPs have now submitted letters of no confidence in her leadership - enough to trigger a formal no-confidence vote.

A government minister as well as a number of Conservative MPs in the pro-Brexit European Research Group, told Business Insider that they believed Sir Graham Brady, chair of the party's 1922 Committee, had received over 48 letters of no confidence.

One senior MP in the group told BI that Brady had received 53 letters, five more than the 48 threshold.

A minister in May's government told BI that they also believed the threshold had now been reached, adding that "even the ERG can't screw it up twice."

The Conservative party chief whip Julian Smith - who is in charge of party management - was seen entering Downing Street late on Tuesday evening, as was the Conservative party chairman Brandon Lewis.

This is not the first time reports of an imminent leadership challenge have circulated in Westminster. Last month similar claims that the 48 letter figure had been reached failed to materialise.

However, May's decision to delay this week's House of Commons vote on her Brexit deal has enraged previously supportive Conservative MPs and appears to have tipped the balance against her.

One ERG MP who had already submitted their letter said they were approached by three MPs who submitted their letters in anger at May pulling the vote on Monday. They added that two of those MPs had been "fence-sitters" who had previously been loyal to the prime minister.

The MP said that a Brexiteer Cabinet minister told them on Tuesday that May would be "gone by Friday."

Multiple publications reported other sources inside Downing Street and the Conservative party suggesting that the threshold for a challenge had been reached.

The respected Sunday Times journalist Tim Shipman tweeted that "conversations have taken place between Cabinet Office and Palace," suggesting that a challenge or even a possible resignation could be on the cards.

If 48 (or more) letters have been submitted, Conservative MPs will hold a vote of no-confidence in May. If over half of Conservative MPs vote against her, there will be a leadership election to choose her replacement.

Any challenge would further delay the already deadlocked Brexit process leading to further calls to either seek an extension, or withdrawal of the Article 50 process, which dictates that the UK must leave the EU by March 29.