UPDATE: The Foreign Office has issued a clarification that UK nationals will be exempt from the travel ban. Read more.
An executive order by President Donald Trump has provoked waves of protest at US airports, where those travelling from seven majority Muslim countries have been detained or turned back.
Signed on Friday, the order has halted the US refugee programme and banned anyone from the countries - Iraq, Iran, Somalia, Yemen, Sudan, Syria and Libya - from travelling to the country, even if they have already been approved for a visa, have an existing visa or a green card.
But it also applies to dual citizens holding a passport for one of the seven and another country, such as Britain.
However, with much of the effects of the order still unclear, there is also suggestion that even those with full UK citizenship but born in one of these countries will not be able to travel.
Tory MP and founder of the polling company YouGov Nadhim Zahawi who was born in Iraq and is a British citizen said he has been advised that he will be unable to travel to the US, where his children are studying at university.
Under tighter rules introduced under Obama, Brits who are a dual national of Iran, Iraq, Sudan or Syria or those who have travelled to these countries along with Libya, Sudan, Somalia and Yemen are unable to travel under the visa waiver programme (WVP) under which most Brits can travel.
Zahawi said he and his wife, also born in Iraq but a British citizen, underwent interviews to obtain a visa to be able to travel to the US under these rules and was happy to do so.
On Twitter late on Saturday night, he said: "I'm a British citizen and so proud to have been welcomed to this country. Sad to hear ill [sic] be banned from the USA based on my country of birth."
I'm a British citizen & so proud to have been welcomed to this country. Sad to hear ill be banned from the USA based on my country of birth— Nadhim Zahawi (@nadhimzahawi) January 28, 2017
But he expressed concern for others "who don't have the platform I have".
"They're British citizens and they should be looked after," he said.
He defended Theresa May's reaction to the ban, which some have criticised for not being made sooner.
"I think her being careful is a good thing", he said, speaking on the BBC's Andrew Marr show.
There has been no update to advice from the government on foreign travel to the US as yet.
In a statement the Prime Minister's spokesperson said the government is "studying this new executive order to see what it means and what the legal effects are, and in particular what the consequences are for UK nationals".
Another high profile name thought to be affected by the ban is star athlete and Olympic here Sir Mo Farah. The star was born in Somalia, is a British citizen and trains in the US.
The sports star has not commented publicly on what this means for him. If in the US currently it would likely mean he would be unable to return to the country if he left. On 20 January, seven days before Trump signed the executive order, Farah tweeted that he was in Ethiopia training for the London marathon. This would mean he wouldn't be able to return to his training camp in the States.
UPDATE: Farah has said the ban is "deeply troubling". Read more.