Everyone visiting the US for 90 days or less must now complete an electronic approval form before departing of face not being allowed on a flight into the country. The Electronic System for Travel Authorization (ESTA), which was originally launched a year ago, becomes compulsory next Wednesday. (January 27)

It applies to all nationals from all of the 35 countries that currently have a waiver status on visas for travel to the US. The approved form is valid form up to two years and allows multiple entries to be made whether for business or holidays.

Airlines, including American Airlines and British Airways, say passengers who have not completed the form will not be allowed to board. The form replaces the green cards that used to be filled in by passengers on flights.

The form takes around 15 minutes to complete on-line and most people should receive approval from the US Department of Homeland Security within a few minutes.  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,' said British Airways director of customer service, Silla Maizey.

'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,' she added.

The scheme is currently free but this may change as the US Senate voted in September to charge visitors from visa waiver countries a minimum of $10 (£7) to fill in the form and enter the country.

There have also been complaints about some travel websites charging to help tourists apply for their Esta, particularly as they are often listed above the official website in internet searches.

This is the free official website for filling out an Esta .