Andrea Leadsom's defection reflects how toxic May has become

A minister resigning from Theresa May’s government rarely makes the front pages these days – since the 2017 election, the prime minister had lost 41 government ministers.

However, there was a sense of surprise in government circles that it was one of May’s more loyal cabinet colleagues, Andrea Leadsom, who became the 42nd – and it is unlikely she will be the last.

Related: Pressure grows on May to quit as Leadsom resigns over Brexit deal

Leadsom’s decision to quit as leader of the Commons comes as May’s premiership enters its final stage. The prime minister is expected to announce her exit date on Friday – and if she fails to do so, then members of the 1922 Committee of Tory backbenchers are likely to change the rules to force her out themselves.

Given the speed at which events are moving, it’s worth asking why Leadsom decided to jump ship late on Wednesday. A committed Brexiter, Leadsom surprised many of her colleagues by sticking it out as long as she did.

She campaigned vigorously for leave in the 2016 EU referendum and has repeatedly raised concerns over the government’s Brexit strategy at cabinet.

Yet unlike her former Brexit colleagues Dominic Raab, Esther McVey and Boris Johnson, she chose to stay on.

However, May’s speech unveiling her ‘new’ Brexit deal proved the final straw. Leadsom was one of a number of ministers to be left dismayed when May appeared to go further in her speech than had been agreed earlier at a cabinet meeting and she believed the prime minister’s promise to give MPs a vote on a second referendum was a step too far.

Given Leadsom’s role as leader of the house meant she would have been the one to announce the withdrawal agreement bill debate in the Commons – at business questions – there was a conflict of interest that prevented her from carrying out her role in good faith.

There is also another factor in all this. Leadsom has made no secret of the fact that she still harbours her own leadership ambitions – announcing recently that she was “seriously considering standing”.

Taking a stand against May’s softening of her Brexit red lines could prove helpful to her in the forthcoming leadership contest – pitching to a Eurosceptic crowd. In the past few days, there has been a change in the mood in cabinet: ministers who previously believed sticking with May was beneficial to their aims now worry that it will make them toxic to the Tory membership.

So, could Leadsom go all the way? In the 2016 contest, she made the final two – and came under a lot of scrutiny. She dropped out following a media storm over comments she made suggesting that her experience of motherhood gave her an edge over the childless May in the contest.

Leadsom has since said the experience has not put her off – telling me earlier this year that it only made her “more determined than ever to do what I can to make this country a greater place”.

Leadsom has lost some of her Brexiter appeal by being in the cabinet. However, she has also gained respect from colleagues for her work tackling Westminster bullying and harassment. Her efforts standing up to the Speaker of the House of Commons, John Bercow, have seen her popularity rise with the Tory grassroots and she topped the Conservative Home cabinet league table in March.

Leadsom is still seen as an outside bet – but then again she was last time.