Following up on a previous topic---
If a US resident transits airside through Heathrow to Paris ( spending 4 hours in heathrow) , is he or she treated/viewed as originating in the USA or the UK.
If we were flying directly from USA to Paris the rules are understandable- vaccination proof and pcr or antigen test within 48 hours ( usa being an amber country).
Do these requirements change because are are transmitting thru London?
Thank you.