UK Muslims 'barred' from US - what we know
A British Muslim family has been prevented from flying to the US for a holiday at Disneyland. Why?
The family of 11 from east London was told just prior to boarding a flight at Gatwick Airport that there was a problem with their visa waiver, but no details were given.
Their local MP has said there is a growing fear among UK Muslims that the US is denying Muslims from entering the country because of their religion, following terror attacks in Paris and in California.
So what is the full story?
What happened at the airport?
Brothers Mohammed Zahid Mahmood and Mohammad Tariq Mahmood, plus their nine children, were heading to Los Angeles from London.
They had all checked in for their Norwegian Airlines flight from Gatwick Airport and were given boarding passes. They had received authorisation to travel under the US Visa Waiver Programme.
But not long before boarding, the nine members of one family were told there was a problem with their visas and they couldn't travel. All 11 decided not to travel.
It is not clear if the issue was related to one family member or several. Reuters quotes a US official saying it was only one person but because the family booked together none could go.
Why were they stopped?
A spokesperson for US Customs and Border Protection refused to comment on this specific case, but told the BBC that people travelling to the US "bear the burden of proof to establish that they are clearly eligible to enter the United States... the applicant must overcome all grounds of inadmissibility".
These grounds include health, criminality and national security.
According to ITV News, a Facebook page claiming links to radical Islamist groups was set up by someone living at Mohammad Tariq Mahmood's postal address. But, the broadcaster said, it appeared to have been set up as a joke.
Mr Mahmood said no-one in his family had any connection to it: "That could be anything, maybe a mistake."
He told reporters the ban could also have something to do with his brother Mohammed Zahid Mahmood once being denied entry to Israel.
Has this happened to other British Muslims?
The family's local MP, Stella Creasy, has said she knows of several other cases and called on UK Prime Minister David Cameron to challenge the US on what she says is the "growing problem" of British Muslims being barred without explanation.
"Nobody knows why these people were stopped. We do know what the common denominator is between them. All of us agree we've absolutely got to be vigilant about tackling terrorism, and we've got to be clear prejudice hasn't got a part to play in that," she said.
Imam Ajmal Masroor said he received similar treatment when trying to travel to the US on 17 December, and was only told his business visa had been revoked.
He said he had never had any problem travelling on that visa before, and feared the US was targeting Muslims.
"This is absolutely discrimination. It is not acceptable and playing into the hands of the terrorists,'' Masroor said.
Is San Bernardino terror attack a factor?
The US relative the two families were going to visit lives in the southern Californian city where 14 people killed in a terror attack by a radicalised Muslim couple in November.
Muhammad Tahir Mahmood, a brother to Tariq and Zahid, told the BBC that he attended the same mosque as the gunman but didn't know him.
What about Donald Trump?
The attack in California sparked a debate in the US about national security.
One of the leading Republicans running for president, businessman Donald Trump, demanded that US borders be closed to Muslims.
His idea was condemned by his rivals and by several global leaders, but British MP Ms Creasy has wondered if US border officials have taken note.
A Muslim campaign group, CAIR, has also said they feel that Mr Trump's policies are being "formally introduced".
But US Customs officials have said "religion, faith, or spiritual beliefs of a traveller" are not determining factors for admissibility.