British officials reacted with concern at the announcement of President Donald Trump's travel ban affecting seven Muslim countries, internal Foreign Office documents reveal.
Emails released to the BBC under the Freedom of Information Act show how officials struggled to cope with the blizzard of announcements issuing from the White House the days after Mr Trump took office.
There was particular concern about Mr Trump's executive order on January 27 temporarily banning visitors from seven Muslim countries just hours after Theresa May became the first foreign leader to meet him in the Oval Office.
Officials feared thousands of UK citizens with dual nationality could be prevented from travelling to the US, amid concerns about the potential impact on Anglo-American relations.
"BE (British Embassy) Washington have been trying to get clarity from State (The State Department) without luck so far," one internal Foreign Office email dated January 28 reported.
"If true, this would obviously mean thousands of dual nationals with British passports being banned from travelling to the US. Not great after the PM visit."
Another email, on the same day, said: "The dual nationals angle will of course be really difficult for us. I'll come back to you when I have more on our response."
The emails show that officials closely monitored media coverage, including Press Association reports of the developing situation, as well as tweets from individual journalists.
One Press Association report picked up by officials highlighted Sir Mo Farah's fears that he may be unable to return home to his children in the US.
"We're still guiding the that we are working with the State dept to establish the impact but grateful if we can be kept informed of any new advice to Brits looking to travel," one official wrote.