[Boris Johnson] will only succeed as prime minister if he broadens his focus and his appeal Guto Harri, former adviser

The questions about his political judgement have been stacked higher by memories of his lead role in the campaign to leave the European Union, which won against all expectations, and later by two years as foreign secretary, his tenure distinguished chiefly by a succession of gaffes and diplomatic banana skins.

To be fair, he wrote his rude poem about the president of Turkey and a goat before he became foreign secretary. He had less excuse for obliquely comparing the EU to the ambitions to dominate the continent exemplified by Napoleon and Hitler.

His mistake in describing Nazanin Zaghari-Ratcliffe - then already in custody in Iran - as teaching journalism in the country was more serious. He was simply wrong. The comments had “traumatic effects” for her, her husband later said, and were used to justify a second court case against her.

A protester holds a picture of Nazanin Zaghari-Ratcliffe, imprisoned in Iran A protester holds a picture of Nazanin Zaghari-Ratcliffe, imprisoned in Iran

Westminster’s longest-serving MP, Ken Clarke, has filled all the most senior jobs in Conservative cabinets save that of prime minister. “[Boris Johnson] was a disaster,” he told me. “The diplomats were driven up the wall. He didn’t read the brief. The only thing he worked at were the photo opportunities at foreign meetings… quite the most hopelessly irresponsible foreign secretary I’ve ever known from any party.”

For an alternative, vastly more friendly view, you might try Camilla Tominey’s in the Daily Telegraph. She hit back at all the “lazy caricatures”, and preferred to remember Johnson’s support as foreign secretary for girls’ education around the globe, as well as his backing for strong sanctions after the poison attack on the Russian defector Sergei Skripal and his daughter Yulia in Salisbury, which resulted in the expulsion of 100 Russian diplomats by the UK and allies including the US. She also drew attention to his habit of delegating tasks to trusted subordinates.

Now, Camilla Tominey is, of course, a colleague of Johnson’s on the Telegraph where he writes a regular and highly prized, highly paid column. Ken Clarke is a known critic of Brexit. My guess is you may already be predisposed to agree with one side or the other.

Either way, Boris Johnson was chosen to serve as foreign secretary not for his diplomatic skills, but because Theresa May wanted prominent Brexiteers in the cabinet jobs most closely tasked with delivering it. That plan didn’t work out particularly well for her.

Brexit ground to a standstill. May resigned, having failed wretchedly to achieve a mission which, in truth, seemed all but impossible from the moment of her disastrous “victory” in the 2017 general election, and Boris Johnson’s rise to replace her is now pencilled into political history. He’ll be hoping it makes easy reading in time to come. Again, we’ll see.

The story of Johnson’s role in the Leave campaign has been told too often to need much retelling here.

There were the two newspaper columns he wrote, one for leaving and one against. The friends (or former friends) like Roland Rudd, the financial PR man who now chairs the People’s Vote campaign, who told me bitterly how Johnson pledged his devotion to the Remain side shortly before announcing the opposite.

Sir Craig Oliver, then director of communications in Downing Street under David Cameron, testifies to a poetic text message from Johnson predicting Brexit would be crushed “like the toad beneath the harrow”, sent moments before he came out for the Leave side.

According to who’s telling the tale, it’s damning evidence that Johnson was never a true Brexiteer with some saying that he joined what he hoped would be the losing side (though still the one most useful to his leadership ambitions) or that he was genuinely torn by doubt until the last moment.

Does the accusation of dishonesty stick? Detractors point to the dubious slogan plastered on the side of the Leave campaign bus suggesting Brexit would free £350m a week for the NHS, and also the alarming suggestion that millions of Turks were waiting to enter the UK and swamp the health service almost overnight. The charge sheet of false or inflated campaign claims, with which Johnson became associated, is a long one.

Of course, Brexiteers are no less vocal in condemning the Remain side’s hair-raising economic prophecies - Project Fear. You will doubtless have your own view.

If Boris Johnson feels any regret - and I have never heard anything to suggest that he does - he has kept it to himself. A friend and close associate told me he is proud of what he achieved, and considers that he “owns” Brexit.

Another friend, his close adviser at City Hall, Guto Harri (a former BBC colleague) told me: “He has to focus very narrowly on the Conservative grassroots now. But he will know that he will only succeed as prime minister if he broadens his focus and his appeal once again way beyond that. It’s something he did pull off as mayor and I just hope he can do that again.”

Johnson may or may not “own” Brexit. He certainly owns the responsibility to deliver it, or to deliver something that works.

His leadership will be unlike anything we’ve seen. But the consequences will be no joke.