Boris Johnson could make more than £5m a year after he leaves Downing Street, experts have estimated.

The figure will be welcome news to a prime minister who is said to regularly complain to friends that he is hard up, citing his second divorce, several children and his reduced income since entering No 10.

In fact, Johnson’s £155,376 salary puts him in the top 1% of UK earners. His housing, transport and a large part of his living costs are covered by the taxpayer.

Regardless of whether his financial straits are real or imagined, there are two certainties, says Tom Bower, one of Johnson’s biographers: that he is hopeless with money and that he will have no problem making lots of it after he leaves office.

“It’s because he’s such a bad money manager that he got himself into that ridiculous situation with the refurbishment of his Downing Street flat,” said Bower. “After that debacle, the financiers who fund the Tory party took him to one side and told him he didn’t need to worry about money; that his future earnings were guaranteed to be so strong that he could take out whatever loans he needed at very low rates.”

Giles Edwards spoke to many former world leaders about their lives after leaving office for his book The Ex Men. He agrees that Johnson’s post-Downing Street earning potential is incredibly strong. “Former leaders are offered everything imaginable for fees that can be nothing short of extravagant,” he said. Johnson’s memoirs alone are guaranteed to earn him in the region of £1m, Edwards estimates.

In Johnson’s backbench days, when he was earning about £830,000 for newspaper columns, books, speeches and TV appearances, he referred to the £250,000 he received for his Daily Telegraph column as “chicken feed”.

But as lightly as he weighed it when he was earning the big bucks, there seems to be no doubt that he and the Daily Telegraph will rush back into each other’s arms the moment his time in office is over.

The biggest bucks, however, are to be made on the lecture circuit: Theresa May has earned more than £2.1m since July 2019. Johnson’s fame means he could demand higher rates, says Tom Clark, a contributing editor at Prospect magazine, especially in the US where Donald Trump has talked him up as a British version of himself. “He has a readymade Trumpian base out there,” said Clark. “But that doesn’t mean the Democrats hate him. He’ll have supporters in both camps.”

The record of those people while in office, it seems, is of little importance on the lecture circuit. Nor is it relevant to corporations prepared to pay half a million or so to former leaders to impress their clients.

“What people in that world have told me,” said Edwards, “is that getting the big names onboard is not necessarily about making connections or generating business in any direct sense. They want to be able to say to potential clients: ‘Would you like the former prime minister to come for dinner?’”

Andrew Gimson, whose second biography of Johnson will be published this autumn, agrees that Johnson’s main money-raising activities will be on the celebrity lecture circuit. “He will be able to command at least £100,000 per speech in America, Japan, China and Australia, and easily do 15 to 20 of those a year.”

But while his record in office might not harm his brand, there is something that might. Sonia Purnell, another of Johnson’s biographers, questions whether Johnson’s two great loves – power and money – could destroy each other.

“There’s a tension here: he doesn’t do resignation but the longer he tries to cling on, the lower his brand sinks,” she said. “The image of his fingernails raking against the wall of Downing Street as people try to drag him out and he’s trying to cling on isn’t good for his brand.”

But there is another reason why Johnson might not be earning big money for long. According to Gimson, his main occupation on leaving office will be trying to get back in.

“Johnson could have made many millions by becoming a TV star like Jeremy Clarkson or Piers Morgan,” said Gimson. “But he chose power over money. I think he’ll do that again. Johnson loves power. I can certainly see him giving it another whirl.”