Why Andrea Leadsom stepped aside for Theresa May

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Media captionTheresa May to take over as Conservative leader

The referendum on our place in the EU was only 18 days ago - longer than a decent summer holiday, but only just. On the eve of the vote we thought that it might change just about everything in British politics, the campaign alone felt like it had thrown everything up in the air. And now what happens next has become rapidly clear.

The result claimed the legacy of our current prime minister, and in less than a fortnight, has produced our next one, Theresa May.

Ironically, given that she's one of the most careful and cautious politicians around and not necessarily a believer in fast decisions, Mrs May will move into No 10 far more quickly than she would ever have imagined, and without having to campaign for the job in the way she and her team had planned for.

By the end of last week she was the clear front-runner, with nearly 200 MPs on board, but many Conservatives felt that their activists around the country could be seriously charmed by Andrea Leadsom.

It looked like the campaign would be closely contested, even though Energy Minister Mrs Leadsom's experience was nothing like her rival's. And of course, in the usual rule in leadership contests, the favourite never wins - in this case, the original favourite, Boris Johnson, had already pulled out of the race. So what on earth happened?

The public reasons are clear as the former contender outlined on the steps of what was to be her campaign HQ in one of Westminster's immaculate side streets.

She said she'd concluded that in the interests of strong leadership, with Theresa May having so much support from MPs and the economy needing certainty in the aftermath of the Brexit vote, it was better to have a rapid transition than a protracted leadership race.

As ever though, one reason does not explain it all, and some of her friends and colleagues have been explaining her other motivations.

She was genuinely taken aback at how her completely accurate quotes were used in the Times story that claimed she believed she was a better candidate to become prime minister because she had children.

There was nothing outlandish about how the quotes themselves were used, although Mrs Leadsom had also made clear that she didn't want the contest to be dominated by her family status.

But it was an early realisation for her that she had opened herself up to a level of scrutiny that was completely new. That followed what she told me was "ridiculous" criticism about her career before Parliament, suggestions that she had doctored or at the very least embellished her CV.

What friends say was the problem, rather than these stories themselves, was how her Tory colleagues, opponents in this contest were willing to use the claims.

Her campaign manager Tim Loughton accused them of "putting smear above respect". Another colleague says she'd been subject to "vile" texts and messages from colleagues; "the abuse was simply too much".

The campaign was worried, with some rivals focused on doing her down, they were worried that if she won, having persuaded the party membership, that she would always struggle to get her MPs on board.

Steve Baker, one of her supporters, told me it was nonsense to suggest that she would become a Tory version of Jeremy Corbyn, but that there were possible "parallels".

It would have been hard for her to govern without reliable backing from Tory MPs, even if the members had been enraptured. As David Cameron has found, a majority of only 12 makes it hard enough to govern, even if the backbenchers are broadly on side.

Her critics will say her decision makes precisely their point. She wasn't ready for the job, and not prepared to put up with its demands. But whatever her true motivations, it is now Theresa May who'll be immediately subject to the kind of intense microscope that only No 10 brings.

The home secretary will go to Downing Street for cabinet tomorrow morning for the last time in that job. The next time her black armoured Jag glides up the street, she'll arrive to walk in as our next PM.

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