Rishi Sunak enters Downing Street with a programme for government mostly written after winning the Conservative leadership at the second attempt.
Mr Sunak set out his vision during his failed leadership bid in the summer, with his economic programme now seen as vindicated after he warned against the tax cuts that brought down Liz Truss.
After Ms Truss resigned, he said he was running again to fix Britain's economy and unite the warring Conservative Party.
"I have the track record of delivery, a clear plan to fix the biggest problems we face and I will deliver on the promise of the 2019 manifesto," he said.
"There will be integrity, professionalism and accountability at every level of the government I lead and I will work day in and day out to get the job done."
Regarded by supporters as a safe pair of hands in turbulent times, Mr Sunak will dust off promises on the economy, energy, defence and crime that Tory members rejected only weeks ago.
Mr Sunak, the former chancellor of the exchequer, put economic prudence at the heart of his summer campaign.
He said he would only lower taxes once Britain had “gripped inflation” — while Ms Truss’s immediate package of tax cuts would not be credible and would push up mortgage costs, he said.
“He was right about the economy during the summer; we need his leadership to get us back on track,” said one Tory MP, Guy Opperman.
Under pressure at the time to offer a more radical vision, he said he would eventually cut the basic rate of income tax from 20 per cent to 16 per cent, but possibly not until 2029.
In other areas, Mr Sunak had a similar vision to Ms Truss. He promised to trim the civil service, push ahead with low-tax freeports — Ms Truss called them investment zones — and make the most of post-Brexit freedoms.
He said he would pressure developers to construct homes more quickly, to “build the next generation of Conservative voters”.
Rishi Sunak through the years - in pictures
Mr Sunak promised to support people through a winter of high energy bills, having criticised Ms Truss for wavering over handouts.
Once in office, Ms Truss changed tack and brought in a price cap, although Jeremy Hunt, the current chancellor, said it would only last until April in his emergency measures to stabilise markets. All eyes will be on Mr Sunak to see if he makes changes to the scheme.
Like Ms Truss, he supported the resumption of shale gas fracking, and called for more nuclear power, offshore wind and North Sea oil and gas exploration.
He said he was committed to net zero emissions by 2050 but would introduce a new target of making Britain energy independent by 2045.
In a play to the homeowning Tory base, he said he would not allow wind farms to be built more easily on the mainland.
Ms Truss’s government, by contrast, announced in its doomed growth plan that planning rules would be relaxed for onshore wind.
Defence and foreign affairs
Mr Sunak is something of an unknown quantity in foreign affairs, having served only in domestic roles in government, but would walk into office amid growing alarm over Russian President Vladimir Putin’s nuclear threats.
In his first campaign, he promised Ukraine that Britain would “remain your strongest ally” in the war with Russia and that his first foreign visit would be to Kyiv.
When asked whether French President Emmanuel Macron was a friend or foe, he had no hesitation in answering friend — avoiding the diplomatic storm that Ms Truss caused by saying the jury was still out.
Unlike Ms Truss, who said defence spending would rise to 3 per cent of GDP, Mr Sunak said he would not set an “arbitrary target”.
But he promised a package of measures to counter Chinese influence in the UK, including by giving MI5 more oversight of businesses and universities.
Another question would be whether to reappoint Defence Secretary Ben Wallace, who is respected in the party but backed Ms Truss over the summer.
Home affairs and immigration
Mr Sunak promised to take the French to task over their efforts to stop migrants crossing the English Channel.
He said he would do “whatever it takes” to start deportations to Rwanda, a scheme bogged down in legal wrangling.
A 10-point Sunak plan on immigration also included tightening the definition of asylum and setting a cap on the annual number of refugees.
Ms Truss had been mulling a more liberal immigration policy to plug economic gaps, putting her at odds with former home secretary Suella Braverman.
In a crackdown on crime, Mr Sunak said in his campaign that he would double the number of foreign offenders being deported.
He said he would go after career criminals by adding a year in prison to any sentence they might receive.