It is now pretty much the standard wherever you go.
This is from the UK Foreign Office website (
www.fco.gov.uk)...
Passports & Visas
Passport Validity
If you wish to travel abroad you must hold a full ten-year passport, even for a day trip. Apply in good time to the UK Passport Office.
Ensure your passport is valid for the duration of your trip. Some countries have an immigration requirement for a passport to remain valid for a minimum period (usually at least six months) beyond the date of entry to the country.
This is a requirement of the country concerned, not the UK Passport Office. Any questions should be addressed to their Consulate or Embassy.
However, this is taken from
www.thailand.com
To apply for a visa, and to check your visa status before travel, contact the Thai Embassy or Consulate in your own country (see list of Thai Embassies & Consulates abroad). [u]
A passport valid for at least three months from your entry date is required for entry into the country.[/U] Once a visa is issued at your country of origin it must be used within 90 days.
As you can see it says 3 months, but maybe this is out of date, it would be worth checking, as it might save you a lot of aggro.
Cheers
Diz