As Nigella Lawson found out last week, gaining entry into the US can prove tricky, particularly if you've admitted to a court that you've snorted cocaine.
Here we outline the different reasons you might be kept out of the country, and look at some of the strangest cases of holidaymakers being turned away at the border.
Why might you be denied entry to the US?
According to the Department of Homeland Security website, travellers may be denied entry to the US for the following reasons:
1. They have previously worked illegally in the US
2. They are suspected of being an intended immigrant who will overstay their visa
3. They are suspected of having ties to terrorist or criminal organisations
4. They have overstayed a previous visit to the US
5. They do not have sufficient funds to support themselves while there
6. On health-related grounds (the Department of State website specifies that this includes anyone with a "communicable disease" or "a physical or mental disorder that may pose, or has posed, a threat to [the person] or others" or "a drug abuser or addict")
And finally, 7. They have been found guilty of a criminal offence
While Nigella Lawson does not have a criminal conviction, the Department of State website also states that entry may be denied to "any alien convicted of, or who admits having committed… a violation of (or a conspiracy or attempt to violate) any law or regulation of a State, the United States, or a foreign country relating to a controlled substance".
The only exceptions are if the crime was committed when the person was under 18 years of age or more than five years before the date of application for admission to the US, or if "the maximum penalty possible for the crime of which the alien was convicted… did not exceed imprisonment for one year". Given that the maximum sentence for someone convicted of possessing cocaine is significantly greater than one year, this would not apply to Nigella.
And clearly, as her case demonstrates, the rules are liable to change. Weeks after her confession, she flew into America on New Year's Day to film a live interview promoting the second series of The Taste USA. So those will a criminal history who had no problem getting in once, may fail to do so on other occasions. Full details can be found here.
Strange cases of travellers denied entry
There have also been dozens of incidents where travellers have been denied entry or even taken into custody for more unusual reasons than Nigella.
In 2012, two British tourists were kept in a cell for 12 hours after landing in Los Angeles and jokingly tweeting that they planned to "destroy America" and "dig up Marilyn Monroe" during their holiday there. Authorities clearly didn't realise that "destroy" is slang for "party".
Abta, the travel association, urged holidaymakers to be "ultra-cautious" when talking about forthcoming trips to the US. "In the past we have seen holidaymakers stopped at airport security for 'joking' that they have a bomb in their bag, thoroughly questioned and ending up missing their flights, demonstrating that airport security staff do not have a sense of humour when it comes to potential risk," it added.
For writing a research paper on drugs
In 2007, Andrew Feldman, a Vancouver professor, was denied entry into Blaine, Washington, after a border agent discovered he'd written an academic paper about taking LSD in the Seventies.
For offending Obama
In 2010 Luke Angel, a 17-year-old Briton, was banned for life from visiting the US for sending Barack Obama an offensive email in which he described the president as "a p****".
For being well travelled
Last year Niels Gerson Lohman, a Dutch writer, was denied entry to the US at the Canadian border after officials found stamps from Muslim countries, such as Yemen and Malaysia, in his passport.
Ellen Richardson, a wheelchair-bound Canadian, was refused entry last November due to being hospitalised for clinical depression the previous year. The decision forced her to miss a 10-day Caribbean cruise from New York.
For playing the guitar
A feature in Vice magazine last year revealed that a German was deported for travelling with his guitar. He said he planned to take part in open mic nights, but officials believed he was planning to seek employment.
For being Yusuf Islam
Muslim singer Cat Stevens, who changed his name to Yusuf Islam, was refused entry in 2004 on "national security grounds". Colin Powell, secretary of state at the time, later apologised.
For criticising the Government?
Ilija Trojanow, a German author, was refused on board a flight to Denver. He said he was not told why, but suggested that his public criticism of the US government's spying operations was to blame.
For relying on Bitcoin
"Doctor Nefario", a Bitcoin developer, was turned away by customs officials in Seattle in 2011 as he only had $600 in cash for a two-month trip. The rest of his funds consisted of the digital currency, but this was not deemed adequate.
For a 24-year-old conviction
The former world's heaviest man, Paul Mason from Ipswich, was recently denied entry because of a 24-year-old conviction for stealing. He had hoped to travel there in order to have surgery to remove excess skin after losing 43 stone.
Other celebrities to have been prevented from entering the US for bad behaviour include Lily Allen, in 2007 after she was arrested earlier that same year for allegedly punching a photographer, Pete Doherty, Amy Winehouse, footballer Jermaine Pennant and Boy George.
How to apply for a US visa
Australian travellers to the US must first complete an Electronic System for Travel Authorization (ESTA). This is an automated system used to determine the eligibility of visitors to travel to the US under the Visa Waiver Program and whether they pose any law enforcement or security risk. The majority of applications are processed within minutes.
Should an ESTA be granted, entry might still be denied. Airlines are required to supply US security officials in advance with details about all passengers so they can be screened. Therefore passengers could be stopped at an Australian or US airport.
What options are available to those denied entry?
Travellers can contact the Department of Homeland Security if they feel they have been unfairly denied entry. They can do this online or by mail, and must supply flight numbers, dates and passport numbers. The application for redress will then be reviewed, but a Department of Homeland Security spokesman said foreigners who had admitted committing drugs offences in the US, or another country, were liable to be refused.
He added: "Depending on the basis of their refusal they may be eligible to apply in advance of travel for a temporary waiver of inadmissibility. The waiver application process can be lengthy."
The Telegraph, London