Ministers have been warned that Britain faces “massive” security risks if Donald Trump is re-elected president this year.
Three of Britain’s former top US diplomats have urged the government to develop contingency plans in case Mr Trump’s bid to return to the White House is successful.
Two ex-Washington ambassadors and a former diplomatic chief said preparations to help the UK cope if Mr Trump were to end US support for Ukraine and withdraw from Nato must be drawn up in secret to avoid giving him a campaign boost.
Despite the legal cloud surrounding Mr Trump’s presidential run, Simon McDonald, head of the Foreign Office until 2020, along with Sir John Kerr and Sir Peter Westmacott, who both ran the UK embassy in Washington, believe a second Trump presidency remains likely.
“We should be thinking through the implications of a second Trump presidency, which are massive,” Lord McDonald told The i.
The threats feared include Ukraine being left exposed if Mr Trump seeks to appease Vladimir Putin over Russia’s invasion, as well as Mr Trump turning his back on the Nato alliance – which he has previously called “obsolete”.
Cross-bench peer Lord McDonald, who was head of the diplomatic service for five years, said: “The impact on the UK is potentially huge.”
“There’s nothing in my lifetime that comes close,” he added, referring to the potential defence and security challenges posed by an ally.
He warned ministers this is “proper preparation time and we should use it”, calling for top meetings in Whitehall and across Europe about “what it would mean for us”.
Meanwhile, Sir Peter, who served as British ambassador to the US from 2012 to 2016, told The i that Britain “ought to be doing some serious homework”.
He added: “There’s not much point in saying, ‘We know he’s a monster, he’s unprincipled, he’s a misogynistic fraud and liar and destroyer of constitutions.’ The reality is: he will be there. We have to find ways of engaging with the US if Trump is elected.”
And Lord Kerr, a cross-bench peer who was Britain’s ambassador to Washington from 1995 to 1997, said Britain and other US allies should “get together discreetly” and remember there is “safety in numbers”.
He feared that any perceived interference in the US election would be exploited by Mr Trump and prove “counterproductive”.
The warning comes as Mr Trump faces several challenges to his candidacy over the 2021 insurrection citing the 14th amendment to the constitution.
He wants to ensure he can appear on 2024 Republican primary ballots in every state, but has been banned from running for office again in Maine and Colorado – both of which he has appealed.
A recent poll shows President Joe Biden losing to Mr Trump in 2024 as Mr Biden’s support among Black, Latino and young voters has dropped.