Kate Fall, David Cameron’s “gatekeeper” and deputy chief of staff, remembers that moment because she was firmly ushered out of the prime minister’s den: “I was told flatly: ‘No. This next meeting – no one else is allowed.’ Senior military official explains the capabilities of the UK’s nuclear trident missiles. The new prime minister is then asked to write handwritten “letters of last resort” to the commanders of the UK’s four Vanguard submarines, with orders on how to respond if the British government is crippled by an enemy nuclear strike. Who will be the next prime minister? Tune in and watch live from 12.30 on Monday as Boris Johnson’s successor is announced. Suddenly, a politician who could always defer to the top has no one higher up to consult. “You’re at the center of the storm,” Kate Fall says of the incomparable pressure of the job. “It’s the tension, the anticipation… You have people coming up all the time saying, ‘Here’s a file. You have to look at it now and make a decision.” As well as making the big speech outside Number 10 (thank the predecessor, set priorities, try to inspire voters), the new prime minister must immediately appoint a cabinet. “It was a surprisingly divisive and unpleasant leadership election,” argues Gavin Barwell, who was Theresa May’s chief of staff. “And I think it’s very important for whoever is prime minister to bring the most talented people into their government and try to bring the party together. “Of course, you have to reward some of your supporters, but when you win you have to be a bit ruthless and think: Now I’m prime minister and eventually I’m going to stand or underestimate the quality of a government. which I put in his place.” Use Chrome browser for more accessible video player 2:41 The Tories are preparing to vote for a new leader Liz Truss looks set to establish herself on the world stage early with an intervention in the UK’s approach to Russia and China. He is also expected to travel to Kyiv to meet President Volodymyr Zelenskyy. However, it is the domestic impact of the war in Ukraine that will be the prime minister’s biggest challenge. “We talk about political honeymoons, but this is a financial nightmare facing the new prime minister,” says Daniel Tomlinson of the Resolution Foundation. “Inflation is already in double digits. Payments are already falling at the fastest rate since the 1970s and things are going to get worse before they get better. Energy bills are on track to top £500 a month in early 2023.” Liz Truss said she would announce her plan to help people with their energy bills within a week of taking office. An emergency budget is expected within the first month. Read more: Who suggests what to tackle rising energy bills The new prime minister also faces an autumn of strikes, growing calls to tackle the NHS waiting times crisis and a predecessor problem: “Boris will be difficult for whoever wins,” says Mr Barwell. “First, if it starts to go badly, there will be a sort of chorus to bring Boris back. Second, we’ve already seen his supporters push for a privilege committee inquiry into whether he was guilty of contempt of parliament to hand himself in. “And third, I suspect he’ll go back to writing a newspaper column. And I can tell you from my own experience when I was chief of staff that those columns are always newsworthy.” Liz Truss or Rishi Sunak will take office with the most troubling economic legacy since Margaret Thatcher. If he loses the next general election, he will go down in history as the youngest prime minister in almost sixty years. It’s an enviable record.