The charge often made against the Cameroons, that they do not in their heart of hearts believe in the modish causes they espouse, is not levelled at Amber Rudd. The new Secretary of State for Energy and Climate Change is agreed, by admirers and detractors, to be a true believer in the science of climate change.

Her appointment was welcomed by the Ecologist, which warned she would face opposition from Conservatives such as Lord Lawson, Owen Paterson and Peter Lilley: “Rudd will have to fight a strategic, robust and constant rearguard defence against those who are ostensibly on her side.”

But she has faced no immediate condemnation from that quarter. This is not just because it would obviously be unfair to condemn her before she has shown what she is going to do. It is also a mark of the high regard in which she is held by many other Conservatives, including some of Thatcherite outlook.

As a leading member of the No Turning Back group told ConHome: “She is one of the most authentic believers in the Cameron proposition.” But, he added, she also recognises (as Tim Montgomerie has pointed out) that the policies which in the general election cut through to the electorate had nothing much to do with modernisation.

This Tory went on to attribute some of the other promotions in the reshuffle to “slavering, mindless sycophancy” to George Osborne, for whom Rudd did indeed have a spell as PPS.

But Rudd’s authenticity saved her from being written off by this Tory as a sycophant. Like many others, he liked her well enough to have gone to canvass for her in her marginal seat of Hastings and Rye, and he said of her in a tolerant tone: “She’s a Macmillanite pragmatist – pretty much like our dear, dear leader.”

When forming a Cabinet, David Cameron pursues an unusual policy. He likes to promote people who know something about the department they are going to run, and then he keeps them there for a good long time. Rudd was an Under Secretary at DECC before making the double jump to become its head.

For those of us who treasure the fine old tradition of throwing ministers into departments of which they know nothing, and moving them on just as they start to understand what is going on, this is a disconcerting process.

Rudd’s predecessors at DECC, Ed Davey and Chris Huhne, were Liberal Democrats, and Conservative energy policy has been described, even by some Conservatives, as “a hopeless mess”, in which contradictory objectives jostle for attention.

But thanks in part to her previous experience, Rudd was able to sound quite lucid when she spoke a few days ago to her local paper, The Hastings & St Leonards Observer: “My ambition in my new role is quite simple: to keep the lights on and carbon emissions down, whilst saving consumers money on their energy bills.”

She followed this up with an interview in the Sunday Times in which she declared: “No more onshore wind farm subsidies and no more onshore wind farms without local community support. That’s going to be one of the first things we’re going to do. I’ve put a rocket under the team to get it done.”

Here is a rocket fired in a direction which shows she is not just some loony environmentalist. In the same interview, she said: “I think women should always be in 50 per cent of places of influence.”

When Rudd says this, it does not just sound like tokenism, and she herself becomes harder to dismiss as a token woman who has been promoted so that the Prime Minister can say a third of Cabinet ministers are women. She carries conviction because she says what she thinks.

This characteristic sometimes gets her into trouble. At the 2005 election, she fought the safe Labour seat of Liverpool Garston, in 2006 she was put on the A list of candidates and selected for the marginal but still Labour seat of Hastings and Rye, in 2010 she won that seat with a majority of 1,993, and in 2013 she gave an interview to the Financial Times in which she said of the constituency: “You get people who are on benefits, who prefer to be on benefits by the seaside. They’re not moving down here to get a job, they’re moving down here to have easier access to friends and drugs and drink.”

That was considered tactless, but has not stopped her winning again this May, with her majority more than doubled to 4,796.

A woman who went to canvass for her in this campaign said: “She’s funny and she’s feisty. She had a huge number of other MPs helping her. When you go canvassing for someone, you really get a feel for who has a good team and a nice atmosphere.

“We went round with two locals, both of them young women, she’d motivated them and they’re both standing for the council. She can’t be pigeon-holed politically. I think she did really get AA Gill on the road to recovery. She’s never complained about being dumped by him.”

Gill was an alcoholic who gave up drink and became, while married to Rudd, a star journalist. They had two children, on whom he dotes, before he walked out on her and went off with Nicola Formby, a model.

Rudd, who is 51, is not one of those politicians who has never done anything before politics. But wherever we glimpse her, we find a kind of buoyant practicality: a refusal to be down-hearted.

Emma Craigie, a writer, was at Cheltenham Ladies’ College with Rudd: “Same house, same year, same classes, so I knew her very well then. There were real problems in the house, there were 17 in our year and a huge proportion developed eating disorders.”

Rudd did not suffer in that way: “She was very comfortable in herself, very warm, outgoing, confident, and very, very competitive. I think she got into a bit of trouble on the day we left school, when she tied together all the chair legs in the dining-room.”

After reading History at Edinburgh University, Rudd joined a bank – J.P.Morgan – which was followed by a spell as a financial journalist, and the foundation of a recruitment agency. Her own father, Tony Rudd, was a stockbroker, while her mother, born Ethne Fitzgerald, was a woman of great energy who served as a magistrate and managed, as secretary of the Kensington Society, to stop the initial scheme for a Diana Memorial Garden in Kensington Gardens.

The Rudds operated on an expansive scale: they also acquired a large house in the country. Amber’s brother, Roland Rudd, is one of the richest and best known people in financial PR. She herself recruited the extras for Four Weddings and a Funeral, in which she can be glimpsed.

If a slight air of unreality hangs over this, it makes it an appropriate preparation for the grand but possibly vainglorious task of passing resolutions to avert climate change.

In November, Rudd will attend a summit in Paris which will attempt to arrive at a global agreement to limit temperature rises to two degrees centigrade.

Rudd knows this project will be viewed with profound scepticism by some Conservatives. But she insists: “I’m going to win them over. This is good for the economy. I approach it with a high moral purpose but also a strong pragmatic one for the economy in terms of building jobs.”

Once again, the fact that she so evidently believes what she is saying may help to carry her through. At the heart of the Cameroon project lies a dual appeal, to both morality and practicality. The task of saving mankind will also, we are assured, create jobs. Green economics are going to make us not only virtuous but rich.

In the affable conviction that they know what they are doing, and vindicated by their unexpected election victory, the Cameroons believe they can dominate politics for many years to come. Rudd epitomises that confidence. She and her colleagues hold the initiative, and they intend to use it.