Donald Trump is a fan of the incoming PM but it is unclear if there will be any real convergence on policy

Boris Johnson has already been dubbed “Britain Trump” by the occupant of the Oval Office, who probably sees it as the highest compliment anyone could bestow. In designating the incoming prime minister a fellow blond “mini-me”, Trump has signalled the US-UK relationship is about to become special in entirely new ways.

There is little doubt that the atmospherics are destined for a dramatic improvement, in the near term at least.

Trump and Theresa May started off well, holding hands in the White House, but that relationship soured as soon as she rebuked him over his impromptu interventions in UK affairs.

Quick guide Boris Johnson's to-do list Show Hide A cabinet reshuffle The first task of any new PM involves rewarding some loyal allies and disappointing more. Several Johnson loyalists have had their eye on the post of chancellor, but only one can do it. A complete clearout of May’s remain-minded ministers provided plenty of opportunity to reward the Brexit believers though. Brexit The issue that will define a Johnson premiership. He has promised to rapidly renegotiate almost all of May’s departure deal, ditching the Irish backstop border guarantee policy – something that would seem a huge task over any timescale, let alone little more than 12 weeks, a fair proportion of which is taken up by a summer break. If this fails, he will be set on a no-deal departure for 31 October, and a likely huge clash with MPs. Iran If Brexit wasn’t enough, a new Johnson government must immediately take steps to make sure he doesn’t begin his time in No 10 with a slide into war. The situation in the gulf is complex, fast-moving and hugely dangerous. Johnson did not cover himself in glory as foreign secretary, especially over Iran. It will be his task to prove he has learned. Managing parliament and Tory MPs Johnson will start as PM with a working Commons majority of four, thanks to the DUP, but within weeks it is likely to be down to three if as expected the Liberal Democrats win in the Brecon and Radnorshire byelection. If this wasn’t tricky enough, a small but significant section of Tory MPs openly detest Johnson, and will not want to help him out - and with his cabinet sackings, the ‘Gaukward squad’ of former senior cabinet members set on blocking a no-deal Brexit swelled in ranks. Loosening the purse strings Such was the fiscal largesse on display from both Johnson and Jeremy Hunt during the hustings process that much as he will seek to kick any decisions towards an autumn budget, voters – especially Tory members – will be expecting both tax cuts and more spending on areas such as education and the police. Everything non-Brexit This might sound glib, but there is a lot to consider – during the three-plus years of Brexit introversion May’s government failed to properly grasp any of a series of long-term, pressing national problems: the crisis in social care; the future of the NHS; a climate emergency; the increasingly insecure future of work; a broken housing market; rampant poverty, including among many working people. This is a huge workload for any new administration. Being prime ministerial Critics might say this is Johnson’s single biggest challenge. The leadership process has shown that while he endlessly harked back to supposed successes as London mayor – an often ceremonial role with relatively few powers – Johnson was notably quieter about his period as foreign secretary. Being prime minister is like the latter, to a factor of 10 – a never-ending succession of red boxes containing vital documents, of urgent briefings, of a whole system hanging on your decisions. Johnson has a tendency to ignore advice, pluck statistics out of the air and rely on sudden, cheap glibness. Curbing these long habits will be a daily struggle - his adopting the acronym 'Dude' in his victory speech shows just how hard it is for him. Peter Walker Political correspondent

Trump appears to have forgiven Johnson for a flamboyant range of past insults, such as the occasion four years ago when the then London mayor said the then presidential candidate demonstrated “a quite stupefying ignorance that makes him, frankly, unfit to hold the office of president of the United States”.

Now that he does hold that office, Trump has decided that Johnson has reformed, and is now the ally who will deliver Brexit where May failed. For now, in the president’s eyes, Johnson is “tough and he’s smart”.

Play Video 0:29 'They call him Britain Trump': US president on Boris Johnson - video

“The personal chemistry between the two leaders is going to be much better,” said Amanda Sloat, a former state department official, now at the Brookings Institution in Washington. “Trump clearly has favoured Boris as leader for a while And certainly he and Boris are going to be very like-minded on Brexit.”

Is Boris Johnson really Britain's Trump? Read more

It is a safe bet that one of the prime minister’s first trips abroad will be to Washington to showcase the new transatlantic harmony, which will be built around flattering a president like no other. The bonhomie is already written into the script. The harder question is whether the new special relationship will involve any real convergence on policy.

However much Johnson may wish to humour Trump, abandoning long-held UK foreign policy positions is a risky strategy for a prime minister with a thin mandate facing the prospect of an early general election. No one wants to go to the polls as Washington’s “poodle”.

But if he does not change policy, the friendly ambience may not last long. Johnson will not be the first leader to find that Trump’s embrace can be a trap.

Facebook Twitter Pinterest Trump and May started off well, holding hands in the White House, but that relationship soured. Photograph: Pablo Martínez Monsiváis/AP

Even as he was hailing Johnson’s victory, Trump gave a shout-out to the alternative waiting in the wings. Nigel Farage was in Washington, and attending a fervent Trump youth rally.

“I know he is going to work well with Boris,” Trump told the cheering crowd. “They are going to do some tremendous things.”

Trump has long touted Farage as a prospective UK ambassador to Washington. Johnson was criticised for failing to stand up for the UK’s ambassador in Washington, Kim Darroch, when Trump launched an attack on him, hastening his resignation. But allowing the president to choose Darroch’s successor is likely to be a genuflection too far.

It is also questionable whether Farage would pass the “developed vetting” required for the post. But Johnson may have to appoint a rightwing political appointee to the Washington job, and hold Farage close, to stop him briefing against his premiership in the White House. The choice of ambassador will be one of the first signs of how Johnson plans to handle the Trump relationship.

Facebook Twitter Pinterest Trump has long touted Nigel Farage as a prospective UK ambassador to Washington, but allowing the president to choose Kim Darroch’s successor is likely to be a step too far for Johnson. Photograph: Tia Dufour/The White House/PA

Even before that, Johnson may have to show his colours on Iran. He arrives in the middle of a full-blown crisis. The UK has seized an Iranian tanker off Gibraltar, on suspicion of carrying oil to Syria, and Iran has struck back grabbing a UK-flagged tanker in the strait of Hormuz.

It is a foreign crisis too many for a prime minister facing the same impossible choices over Brexit as his predecessor. It will be tempting to look for a swift way out, exchanging tankers, and perhaps embracing a broader deal, release frozen Iranian funds and win freedom for a British-Iranian woman, Nazanin Zaghari-Ratcliffe, and other dual nationals being held as bargaining chips by Tehran.

Facebook Twitter Pinterest Boris Johnson and the Iranian foreign minister, Mohammad Javad Zarif, in December 2017. Johnson mistakenly said Nazanin Zaghari-Ratcliffe had been ‘teaching people journalism’ in Iran. Photograph: Abedin Taherkenareh/EPA

It would be an act of redemption for Johnson, whose gaffe while foreign secretary, mistakenly saying Zaghari-Ratcliffe had been “teaching people journalism” in Iran. She had been on holiday, but Johnson’s mistake deepened her problems with Iranian prosecutors, who portrayed her as a propagandist.

A neat resolution with Tehran would not go down well with the hawks in the Trump administration, however.

The UK, along with other US allies in Europe, have been under sustained, mounting pressure from Washington to join its campaign of “maximum pressure” on Iran, but they have kept faith with the nuclear deal they made with Tehran in 2015.

The rift has cut deep. The days are long gone when the UK could claim to have a seat at the table when foreign policy is made in Washington. The special relationship in that sense may never return. But Washington now often skips even the niceties of alliance. The secretary of state, Mike Pompeo, made it clear after Friday’s seizure of the British tanker, the Stena Impero, on Friday, that it was up to Britain to protect its own ships.

The crisis in the Gulf could even present an opportunity for the new prime minister. Unlike Bolton and Pompeo, but like the UK, Trump is anxious to avoid a conflict. Some creative diplomacy on Johnson’s part could open a face-saving option for the US president and Tehran to abandon the collision course both sides are locked into.

“President Trump seems more interested in a win than a war, and may want to help Johnson get off to a good start,” said Peter Westmacott, former UK ambassador to Washington. “Just maybe, there could be a new, collaborative approach towards Iran, which would make it worth Tehran’s while too to engage, despite the economic and other pressures they are under. Might be worth a try.”

It is the sort of long shot that an incoming prime minister with no other major foreign policy challenges in his in-tray might attempt. Johnson perhaps does not have that luxury.

It is hard to identify much wiggle-room on other major issues that divide Washington and London. The UK is not about to join the US in leaving the Paris accord on the climate emergency. Moving the British embassy in Israel to Jerusalem and adopting the Trump administration pro-Israeli positions would entail tearing up decades of UK policy in the Middle East.

Johnson could comply with US entreaties to exclude the Chinese company Huawei from the 5G telecoms market, but that would mean blowing up the relationship with Beijing. Johnson went out of his way to tell a television interviewer on Tuesday: “We are pro-China.”

Both Johnson and Trump will talk up the possibilities of a US-UK free trade agreement post-Brexit, but the realities of the negotiations are likely to be unsentimental at best. Trump’s “America First” approach leaves no space for sentimentalities of friendship, and Congress will not ratify any trade deal if Brexit jeopardises the Good Friday agreement.

Just ask Shinzo Abe, who has assiduously courted the president and his family, only to be casually humiliated. Trump dispatched the Japanese prime minister on a peace mission to Tehran, but then disowned the effort when it failed. Then, on the eve of a Japanese-hosted G20 summit last month, the US president called into question the US-Japanese defence alliance.

In setting his transatlantic course, Johnson will have to take into account that loyalty to Trump is rarely reciprocated.

“I don’t think it is going to go particularly well, to be honest,” Thomas Wright, the director of the centre on the US and Europe at the Brookings Institution, said. “I don’t see Johnson throwing a switch and saying we are now aligned on foreign policy. And I don’t see Trump changing his transactional view of the special relationship.”