Holidaymakers travelling to the USA will have to fill out an online form before travel in a new system of checks that become mandatory from today.
The Electronic System for Travel Authorisation (Esta) can take up to 72 hours to be approved and gives tourists entry to America.
Airlines have this week warned that they will not allow passengers to board flights who have failed to fill out the online form.
The electronic approval replaces the green cards that passengers used to be given to fill out on the plane before landing.
The scheme officially came in a year ago, but it has become compulsory from today.
Most passengers will receive approval within minutes of filling out the form, but British Airways and American Airlines are advising everyone to apply 72 hours in advance.
British Airways director of customer service, Silla Maizey, said: “It only takes 15 minutes to complete an Esta and the vast majority of applicants will receive approval for travel within minutes, although it can take up to 72 hours.
“Under the new regulations, we will not be able to accept US-bound customers for their flight if they have not received Esta approval or if they do not hold a valid visa or Green Card. Most of our customers are already familiar with Esta as it has been in place for more than a year, although not fully implemented.”
Once the Esta has been approved it is valid for two years and can be used for multiple entries into the US.
The new online entry application does not just apply to the UK, but 34 other nations with US ‘visa waiver’ status.
The quantity of websites charging to help tourists apply for their Esta is causing confusion, particularly as they are often listed above the official website in internet searches.
The free official website for filling out an Esta is https://esta.cbp.dhs.gov
However, in a controversial move, the Esta may not be free for much longer.
The US senate voted last year in favour of charging visitors for filling in the form.
Secondary approval from the House of Representatives could see the charge of at least $10 – £7 – being brought in as early as this summer.