Liz Truss: What sort of prime minister will she be?

A heavy burden of responsibility falls immediately upon the shoulders of any new prime minister, often causing a silent quiver of nerves. For Liz Truss, self doubt does not form part of her lexicon.

People who have met her in recent days say she is relishing the ride and is brimming with self-confidence.

But even the UK's new prime minister might admit in private that what she describes as "eye-watering" energy bills will present her with a hefty challenge, unprecedented since her hero Margaret Thatcher assumed office nearly half a century ago.

When Lady Thatcher moved into Downing Street in 1979, the country had a good idea of their new prime minister. She had been leader of the opposition for four years.

While Truss has been a cabinet minister for eight years, she has had a lower profile than Thatcher. And even those who know the foreign secretary are wondering what instincts she will follow.

Will we see the return to the fore of the pragmatist who moved seamlessly from the Remain camp to the warm embrace of the Brexiteers? Or will she govern in the mode of her leadership campaign - a lady not for turning, in the words of Thatcher, who will focus on tax cuts?

Over the past few days, BBC Newsnight has been speaking to people who know Truss to assess whether her past can tell us about her future. The consensus seems to be that we will see Liz Truss turning to both sides of her political past to guide her thinking.

Over the weekend Truss announced that within a week of taking office, she will outline an emergency plan to help people with those energy bills. But in a "fiscal event" later this month, her new chancellor will outline a "broader package" that will hold fast to her campaign pledges.

Baroness Morgan of Cotes, who entered parliament with Truss in 2010 and who served with her in cabinet, says we will see the two sides of the new prime minister's character in response to the energy crisis.

"I think that there'll be a combination of approaches," Baroness Morgan tells Newsnight. "I think people are going to find it's quite hard to pigeonhole Liz in many ways."

Paul Goodman, editor of the ConservativeHome website and someone who knew Truss during his time as an MP, says the new PM will need to put the UK on a war footing to both meet the energy crisis and to shore up her political support.

"The key to Liz Truss over many years has been her adaptability," he says. "So although she has this reputation as an ideologue and she has very clear ideological roots - originally as a Liberal Democrat - she is somehow the darling of Leavers who in the referendum was a Remainer.

"She is the champion now of the Tory right, having once been a Liberal Democrat. And she's presented herself in this election as the new kid on the block when she's actually been in cabinet for the best part of 10 years. So she has extraordinary powers of reinvention and recovery."

But there could be political trouble in embracing strong state support to help people with energy bills. "The difficulty for her would be this: among the people who elected her are a large body of people who want a different approach," Goodman says.

"So she would have to fall back for support on the body in the Conservative party that didn't vote for her, while irritating, if not angering, some of those that did. And that's going to be a very difficult political horse to ride."

An unlikely political mentor sees a more ideological figure. Lord Robertson of Port Ellen, the former Labour defence secretary, encouraged Truss to pursue a political career when she was head of government relations at Cable & Wireless, where he served as a board member.

"Liz is somebody who gets on well with people," Robertson said. "She has become much more ideological since the days when I would meet her occasionally in the House of Commons… I think she's going to turn out to be quite an ideological fixed-view person in No 10."

Robertson knew her as a conventional budding politician who had attended Oxford and who would soon enter the world of Westminster think tanks. That conventional path was pursued in parliament when Truss followed David Cameron's lead in supporting Remain in the referendum.

The careers of many Tory Remainers were destroyed by that referendum. But it was the making of Truss.

In the aftermath of the referendum she intuited what would happen at the time when it was a genuinely open question about what sort of Brexit we'd end up with. "The Leavers will win because they care more," she told friends.

That was a political judgment which led her to make an emotional commitment - she would throw her lot in with that side, lock stock and barrel.

Mr Goodman says her change of tack is more complicated than a simple case of a pivoting politician. "My memory of the time is of a certain vibe emanating from Liz Truss which is: 'What's all this got to do with me? I'm trying to get on my with my job as [environment secretary] and this referendum seems to me a massive distraction from it.'"

He added: "So I don't feel it was just about pleasing the powers that be. But what happened then shows her powers of adaptability."

Changing her mind is constant theme for Truss, who was an active Liberal Democrat at university. But her passion for politics, influenced by her left-wing activist parents as a child, has also been constant.

Truss's success has led to something of a family split. Her mother Priscilla has put family ties before politics and is enthusiastically supporting her daughter. But her father John, a maths professor, is less reconciled to the idea of his daughter as a Tory prime minister, according to her friends.

But Liz Truss does take one core gift from her father into Downing Street: a passion for maths. And anyone invited to an interview with the prime minister had better expect a tricky maths challenge.