To say that I have doubts about Theresa May is an understatement. Even when I tipped her in 2011 as the most likely compromise candidate to succeed David Cameron, it was clear that she ran what might politely be termed a closed operation, with a small team prone to extreme paranoia. Beyond getting to the top it is unclear whether Mrs May offers anything resembling a coherent agenda – on education, social reform, the constitution, defence, foreign affairs and Europe.

‎But it is clear that she is one of the few grown-ups left in the room. Partly for that reason, it is absolutely essential that Theresa May wins the Tory leadership contest and becomes Prime Minister. The alternative is Andrea Leadsom, who will now face May in the final two that goes to the Tory membership this summer. In the vote of Tory MPs, May got 199 votes and Leadsom 84. Gove crashed out with 46.

Leadsom must under no circumstances be allowed to become Prime Minister, particularly when the UK faces such historic challenges.‎ Here is why I have come to that view, and it not just because there is nothing in her political track record which suggests she is ready to run the country.

I should say that in my few encounters with her I have always found Mrs Leadsom to be pleasant. We were on the same panel at a Tory party conference fringe event several years ago, and she was a leading presence in the Tory Fresh Start group which attracted a lot of journalistic attention a few years ago. She claims now to have set that group up, which is news to the other founders, I understand. She is a nice person with an ambitious streak. It’s not a crime.

But all along I’ve had uneasy feeling about her credentials to lead or be a cabinet minister. In Select Committee hearings as a new MP she seemed a little too fond of bigging up her role as an alleged City hotshot. The questions she asked were just a little too focussed on grandstanding. Leadsom’s routine never quite rang true.

My doubts crystallised at a party on Saturday when one of Leadsom’s team – an MP – told me that she had “got to the top in the City.” That is what is known, technically, by anyone who knows about the City, as total balls. Another MP, who had never mentioned her to me before, said “she is the new Thatcher.”

A third Tory MP, deeply sceptical of Leadsom, said that he was worried because in a meeting with her after the referendum she had been “Panglossian” in her dismissal of the negative effects of Brexit – in the short-term – on the City and economy, and she seemed to have no practical ideas on how to respond and mitigate the shocks.

I came back to London resolved to pay particularly close attention to the leadership contest and to the claims of the contenders. The Tory contest is a serious business. The Tory party is choosing us a Prime Minister and Lord help Britain if they pick someone not up it.

I was then contacted by a former colleague of Leadsom’s from her time in business. He had been fascinated by her rise in the referendum, and since it astonished by the claims made by her supporters. He checked out her wikipedia and Who’s Who entries and found an alarming discrepancy.‎ He succeeded in getting her to make an important amendment.

I made some enquiries and then ran his letter on Reaction, and offered Leadsom’s team a right of reply. Since then others in the media have discovered further troubling details that do not fit with Leadsom having “got to the top of the City”.

After we broke the story, I offered a right of reply and was told that “Andrea says it is nonsense.” Sensibly her press team, which has been around the block, promised to get me a full CV from Leadsom.

What arrived the next day did not answer all the doubts. Indeed, it even raised fresh questions. What this was not by any stretch of the imagination was a full CV that anyone seeking a job would provide to a potential employer, let alone to a country seeking an account of a potential leader’s record. It was a thin list with very little explanation. My cats have more detailed CVs.

If you are Tory MP or member and you do not think this matters, then you need your head examined. We all make mistakes in life, but we are not all running to get our hands on the nuclear codes and the economy.

As I say, Mrs Leadsom is a nice person and she may well be a good MP. But that is not enough to qualify someone to lead the UK at a crucial moment in its history. It looks as though she and her team have got carried away in the moment. Wanting to prevent a Remainer – Theresa May – becoming Prime Minister they have projected their hopes and ideological desires on to Leadsom, and when scrutiny (of the kind a leader must expect) has been applied some of them have responded with post-truth witterings about it only being a CV.

Meanwhile, Leadsom has allowed the impression to be created that she was a bigger figure in the City than she was. She could have clarified all of this at any point in the last few years, but sadly she did not. In reality, she had a perfectly successful middling career in the City that needed no exaggeration and of which she can be proud. But over the course of several years she allowed it to become something else in parliament and on the media. Her own assertions – even in recent days, about the scale of her management experience – made the situation worse. Such a person must not become Prime Minister.