BBC News Online spoke to US and UK authorities to clarify who is affected and what they will have to do.

Who is affected by the new rules?

Those who have to renew passports after 26 October this year, but before new biometric ones become available in mid-2005.

Also those with non-machine readable passports that were obtained at overseas British missions.

Why is the US imposing this change in its visa-waiver scheme?

The move is part of America's toughening of measures designed to protect it against further acts of terrorism.

The US wants to be able to instantly check a visitor's criminal background at 115 airports handling international flights and 14 major seaports.

Homeland Security Secretary Tom Ridge said the US aims to be "open to visitors, but closed to terrorists".

How do I get a non-immigrant visa for the US?

By applying to a US embassy or consulate. Visas currently cost �67.

Details are availabe on the website: www.usembassy.org.uk.

Applicants can also call 09055-444-546. Calls are charged at �1.30/min.

Written information is available from: The Consular Information Unit, US Embassy, 24 Grosvenor Square, LONDON W1 1AE. Enclose an SAE.

Applicants will need to complete an application and attend an interview.

How will children be affected?

If they are aged 16 or over, they have to hold their own passports and cannot travel on their parents'.

What is a biometric passport?

A biometric passport contains an electronic microchip that holds information on the passport holder.

The US requires at least a facial image to be included. The UK is carrying out tests to include fingerprints and eye recognition data.