https://www.gov.uk/government/world/organisations/british-embassy-bangkok
Emergency Consular Assistance (24 hours)

For emergency assistance, such as in the event of the death, assault, arrest or hospitalisation of a British national, call the embassy on +66(0)23058333 and follow the instructions to be connected with consular officers. If you are calling from the UK about a British national in Thailand, call our Consular Assistance Team in London on +44(0)2070081500