Do I need to send all paperwork for a tourist visa from the U.K. or just the passport?

When applying for a tourist visa to Thailand from the U.K., it is generally required to send only the passport, along with the payment confirmation that includes a barcode, and a prepaid return envelope. Some users recommend sending additional documentation just in case, such as copies of other relevant paperwork. It is also noted that the issuing of tourist visas by the Royal Thai Embassy in London may be subject to current travel regulations.