Dual Nationality
If you have a British passport or UK travel documents but you are a national of the countries listed below, you cannot enter Thailand on visa exemption.
You have to lodge an application for a Thai visa in person at the Royal Thai Embassy in London.
The countries are: Afghanistan, Algeria, Bangladesh, Cameroon, Central African Republic, China, Democratic Republic of the Congo, Republic of the Congo, Egypt, Equatorial Guinea, Ghana, Guinea, India, Iraq, Iran, North Korea, Lebanon, Liberia, Libya, Nepal, Nigeria, Pakistan, Palestine, Sao Tome and Principe, Sierra Leone, Somalia, Sri Lanka, Sudan, Syria, and Yemen
If you own a residence status in the United Kingdom or Ireland, The Royal Thai Embassy in London shall issue you a visa, provided you have a passport from the above-mentioned nations.