My apologies if this has been previously asked,  but I'd appreciate any recent clarifications available.

 

Is it 72 hours prior to the flight departure,  or,  72 hours prior to UK arrival which is required.  

 

Regards.

Before you leave for the UK

Everyone travelling to the UK must:

• book at least one coronavirus (COVID-19) test for after you arrive
• provide your contact details by completing the online passenger locator form
• provide proof of a negative COVID-19 test taken in the 3 days before you leave for the UK

 

https://www.gov.uk/uk-border-control

That was my understanding also.  However I had seen information that contradicted that, but couldn't track it down again.  I have now however been able to determine the full answer which is as follows:

 

The test must have been taken at most 3 days before departure of the last direct flight to the U.K.

 

So the answer above is correct if flying directly from BKK to UK but if transiting via a European airport, it can be 72 hours prior to the departure of your final leg.

 

I hope this clears things up for any UK bound passengers.