Explainer: How serious is the US-UK ambassador row?

Britain and the US have been plunged into a full-scale diplomatic dispute, centred on Kim Darroch, the UK ambassador to Washington.

On Tuesday, Donald Trump used Twitter to denounce Darroch as a "very stupid guy", while Theresa May told her cabinet that her ambassador was a "highly respected" civil servant.

Why has Britain’s ambassador incurred Trump’s wrath?

The spat stems from the leak of confidential diplomatic telegrams written by Darroch to senior ministers over the past two years.

In the telegrams, obtained by the Mail on Sunday, Darroch described the Trump administration as “dysfunctional”, “faction riven” and “inept”.

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Trump came close to declaring Darroch persona non grata on Monday by saying he would “no longer deal” with the UK ambassador.

Is May standing by her ambassador?

May, who will step down as prime minister later this month, has given Darroch her “full support”, according to a Downing Street spokesperson.

"The PM is playing it as robustly as necessary right now, which is to stand by her man," said Robin Niblett, director of Chatham House, a think-tank. "In her final days at Number 10, May has effectively thrown herself up as a heat shield for the next administration."

However, some MPs noted May has said nothing publicly in defence of Darroch, and a Downing Street spokesperson said on Sunday she disagreed with her ambassador’s critical judgments on the president outlined in the leaked telegrams.

"I don't think May disagreeing with what was in the telegrams was very helpful to Kim," said a former Whitehall official.

Darroch's withdrawal from a meeting on Tuesday between Liam Fox, UK trade secretary, and Ivanka Trump, the president's daughter and a White House adviser, is also likely to go down badly in parts of the UK civil service.

“The UK shouldn’t give the impression it is taking orders from the White House on when our ambassador can accompany ministers and when he can’t,” said the former Whitehall official.

If Boris Johnson succeeds May, will he stand by Darroch?

It is unclear precisely what Johnson, the frontrunner to be the next prime minister, will do, particularly given Darroch’s ambassadorial term is due to finish at the end of the year.

Even before the current row broke out, there were strong indications from Johnson's campaign team that he would move Mark Sedwill, the cabinet secretary and head of the civil service, to Washington to replace Darroch at some point in 2020.

“It’s very difficult to imagine Kim in his post after January,” said one Whitehall official. “There was some talk he would stay on but that has ceased.”

There is speculation at Westminster that Johnson could appoint a political figure to the Washington embassy as ambassador. But allies of Johnson vehemently reject the idea he would choose Nigel Farage, leader of the Brexit Party, even though he is a friend of Trump.

In Tuesday night's head-to-head leadership debate, Jeremy Hunt criticised Trump and promised to leave Darroch in his post until he is due to retire early next year, adding that no other country could determine who Britain sends as its ambassador.

"If I am the next prime minister, the ambassador in the United States stays because it is our decision," he said.

Johnson refused to offer that commitment, trumpeting instead his friendly relations with the US president.

Will the US administration refuse to deal with Darroch in any way?

The White House followed through on Trump's tweet that he would not deal with Darroch by withdrawing an invitation to the UK ambassador to attend a dinner that US treasury secretary Steven Mnuchin hosted for the Emir of Qatar on Monday evening.

One person briefed on the matter said Mnuchin’s decision was in the best interests of the UK since Darroch would have found himself in the same room as Trump.

US officials said the brouhaha would dissipate once another big story started to dominate the headlines.

Several noted that Washington has had its own version of such embarrassments, with the WikiLeaks dump of US diplomatic cables almost a decade ago.

However, Tom Wright, a foreign relations expert at the Brookings Institution, said if Trump enforced the tweet it would "effectively PNG" Darroch. "He is not deported but he cannot do his job."

Another former Whitehall official said: “[The White House] could try and shut Kim out but it’s tricky. We’re a friendly nation and there are large reaches of the US that are not under White House control, such as Congress, business, mayors, think tanks and so on. But the White House can shut out central parts of the administration and, if that happens, London would have to think about whether it’s feasible to keep Kim there.”

What impact will this spat have on UK-US relations?

While the UK and the US generally have a close relationship, the dispute comes amid tension between the two countries because Britain is proposing to allow Huawei, a Chinese telecoms equipment maker, to supply parts of a next generation mobile phone network in spite of Washington concerns it could be used for spying by Beijing.

The row could also complicate efforts by the UK to forge a free-trade agreement with the US after Brexit.

While May has had a fraught relationship with Trump, the president gets on with Johnson, and the favourite to be the next prime minister has the opportunity to reset relations.

Some former officials play down the likely impact of the dispute. "I don't think the disagreement will have a huge effect in the long run," said Peter Ricketts, a former head of the UK Foreign Office. "The history of these sorts of things . . . is that although there is short-term irritation, the bilateral relationship is defined by long-term priorities. Ultimately, what happens on trade policy, Russia, Iran and climate change will shape the relationship far more."

But other former officials fear the row could spiral out of control. Tom Fletcher, the UK's former ambassador to Lebanon, said: "The hope was that this could be contained. But president Trump's bizarre tweets have clearly escalated. It is now bigger than an unfortunate leak." – Copyright The Financial Times Limited 2019