The flight time from Thailand to the nearest airport in the UK (which would be in England in your case) is approximately 11 hours and 40 minutes.
Your question does not contain enough information for an accurate answer. The United Kingdom is made up of four countries, several islands and dozens of overseas territories. You will have to ask the question again giving an exact location for an accurate flight time.
The flight time is approximate. Factors such as weather conditions could alter the length of the flight.
Flying time depends on where you want to fly FROM, this is not a complete question.
For direct flights, about 8.5 to 9 hours flying time.
The flight time from Auckland Airport to Thailand is about 12 hours, 4 minutes.
The flight time from Bangkok, Thailand to Phuket, Thailand is abut 51 minutes.
The flight time from Bangkok, Thailand to Singapore is about 1 hour, 46 minutes.
The flight time from Bangkok, Thailand to Germany is about 11 hours, 6 minutes.
A typical flight between Thailand and Brazil would have a flying time of about 21 hours, 27 minutes.
A typical flight between Thailand and Fiji would have a flying time of about 11 hours, 33 minutes.
The flight time from Detroit, Michigan to Bangkok, Thailand is about 17 hours, 8 minutes.
The flight time from Bangkok, Thailand to Sydney, Australia is about 9 hours, 21 minutes.
The flight time from Bangkok, Thailand to Melbourne Airport is about 9 hours, 7 minutes.
The flight time from Bangkok, Thailand to Madrid, Spain is about 12 hours, 40 minutes.
The flight time from Cairns, Australia to Bangkok, Thailand is about 7 hours, 29 minutes.