It was billed as “the march of the women” but David Cameron decided well before this month’s ministerial reshuffle that one woman in his cabinet was going nowhere: Theresa May.

After two remarkable months in which the home secretary has added an unpredictable ruthlessness to her political armoury, the prime minister and his allies are both respectful and wary of May, the most powerful Conservative woman since Margaret Thatcher. “One of the central principles of the reshuffle was that Theresa must not be promoted,” says one official close to Cameron.

Theresa May this month became Britain’s longest-serving home secretary in more than 50 years, establishing a reputation for cool competence that has won her admirers across the party and made her the bookmakers’ favourite to succeed Cameron as Tory leader.  Theresa May