All Britons travelling to the US without visas now need machine-readable passports under newly-introduced rules.
Machine-readable passports have two lines of code on the photo page
Almost all British passports issued since 1991 are machine-readable, indicated by two lines of coded data at the bottom of the photo page.
However, the requirement could affect children travelling on a parent or guardian's passport, as they will now need separate documentation to enter.
Britain is one of 27 countries affected by the rule, an anti-terrorism measure.
Travellers who do not have a machine-readable passport will have to apply for a visa to enter the US.
If they arrive in the US without the correct documentation, they will be given a one-time exemption in the form of a letter explaining their documents need to be changed.
Their passport will also be stamped to show they have been warned.
British Airways' James Forster said families should check they have the correct documents "to make their journey as stress free as possible".
The documents have been issued in Britain since November 1991, and holders can travel to the US without a visa for the 10-year lifetime of the document.
Mr Forster, British Airways' government and industry affairs manager, remained optimistic that the changes made by the US State Department would not cause too much disruption.
"We hope that, as the UK has been issuing machine readable passports for the past 10 years, most of our UK-based customers will be OK.
"However, we believe that many families may fall foul of the new rules as the children have traditionally been placed on their parents' passports rather than having their own."
However, British Airways would allow passengers without machine-readable passports to board flights to the US because the US authorities were allowing a one-time exemption.
Children born after 5 October 1998 are issued with their own passport, but many children born before that date were included on an adult's passport.
Under UK law, they must get their own passport when they turn 16, the passport on which the child travels expires, or the adult's passport is submitted for amendment.
British passenger Marcus Goodwin said he was unaware of the new US rule, but is not expecting any problems as his 15-month-old son has both a US and a UK passport.
"You would assume [passport regulations] were going to stay the same, unless there had been an enormous advertising campaign. I haven't seen anything," he said.
The fastest a passport can be issued in the UK is 48 hours, with the usual time being about two weeks, the Passport Office said.
The machine-readable passports, standard issue in most countries, contain lines of coded data usually beneath the passport photo which can be swiped at airport check-in and at US immigration.
It allows the information on the passport to be immediately cross-checked against databases run by the US security services.
Most countries in the European Union are affected by the new rules as well as Australia, New Zealand, Japan and Singapore.
The changes are being driven by the US department of homeland security and the State Department.
They say they need as much information as possible on every visitor to the US to help ensure the safety of American citizens.
Have travelled 6 times this year to the States, I have a machine readable passport so no visa required. However, since my last trip the finger print and picture requirement has come in. Found to my pleasant surprise that getting in was even more straightforward. The staff at Detroit Airport could not have been more efficient, helpful and courteous.
Andrew M. Bull, Kettering, England
Unlike other ex-pats, my passport issued overseas (this year in Canada) is machine readable. However, I would caution people about rushing to renew their passport because another change is on the way: passports with biometric information. If you can wait it out then do so!
Malc, Toronto, Canada
The British Consulate in Washington DC currently issues machine-readable passports, charges about 80 US dollars and turns them round in under a week. Far quicker and easier than I ever managed to do it in London!
Gary Brown, Dallas, TX, USA
I went through JFK 2 weeks ago. My machine readable passport didn't read and was typed in by hand. Then the fingerprint machine wouldn't work either despite being told to press harder and harder on the scanner. I have no idea if the photo worked but I'm sure all the kit was really expensive.
Dave, London, UK
Even with a machine-readable passport you may still need a visa! A Brit flying directly from UK to US gets a visa waiver, but I got caught out when I flew to Canada then tried to drive my rental car into the US. Without a visa you will have to pay (in cash) to get into the country.
Joe Harrison, Bracknell, UK
Having had my latest passport renewal issued by the British Embassy in Tokyo, (at an unjustifiably extra cost) I also do not have the requisite coding to enter the US. Looks like I won't be going for another 8 years now!
Adrian, Osaka, Japan
My passport was issued by the British High Commission in Barbados two years ago and is valid until 2011. Unfortunately it is not readable and I will have to pay (again) to get another new passport. I am not sure when I will be able to get this done as I'm not sure when I will get the time to stay in the UK for a long enough period to get it processed. The whole fiasco is frustrating and expensive!
Abigail, Strasbourg, France
As a Briton in Kuwait, with a passport issued by the British Embassy in Kuwait (at a hugely inflated cost) my passport does not have the 2 lines of coding. I cannot visit the USA without a visa, that is a 2-3 month process here. So I guess I have been affected.
Neil Forrest, Kuwait
Just checked my passport which was issued in 1999 at the British High Commission in Kuala Lumpur... yes, you guessed, it is not machine readable! So, should I wish to travel to the US, then YES, I have been affected. To change the passport (if possible) will probably be a costly affair based on the hugely inflated cost of issuing my last passport here... and this passport still has 6 years validity!
Mark, KL, Malaysia