It's all part of the wave of legislation enacted after the September 2001 attacks on New York and Washington, DC, the aim of which is essentially to make it more difficult for terrorists to attack the USA. Whether or not it does that, and whether the burdens it places on legitimate travellers and 'ordinary citizens' are worthwhile, is a source of some contention, but outside the scope of Windows Watch, if we're honest.

One particular source of confusion is particular to journalists, who require a special visa (called an I visa) to visit America for work. Where it gets tricky is that, if you have an I-visa, or other nonimmigrant visa, and you're travelling to the USA but not for work, you need to travel under the Visa Waiver Program instead.

Although the whole thing can be quite confusing, there's a lot of information on various official American websites concerning the process and how it works. But one thing we couldn't figure out from all the documentation was whether or not we needed to fill in an ESTA application even if we already held a valid visa (given that the American Department of Homeland Security already has all the relevant information from the visa application).

In the end, we spoke to the press office at the US embassy in Grosvenor Square, which answered the question straight away: you do need to fill in the ESTA form even if you have a valid nonimmigrant visa, if you're travelling to the United States of America for leisure rather than work.