I am coming from the USA, transiting through Heathrow Terminals 5 to 3 and on to France; will I need to prove I took a Covid-19 test in the US and it was negative? Will I need to show it to British Airways before I get on the plane to London?
That IATA link only offers 3 European countries in the drop-down menu—-Belgium, Bulgaria, and Liechtenstein. Is there. Way to change it to show more?
try this link https://www.iatatravelcentre.com/world.php
Here’s a link about transiting through Heathrow. It should answer all your questions.
Are you vaccinated?
If yes, you do not need to take a test prior to boarding.
For the UK, you will need a passenger locater form filled out no more than 48 hours prior to your arrival in the UK. You will also need to show proof of vaccine. (If you were staying in the UK, you would have to arrange and pay for a Day 2 test. But you are just transiting so you don't)
For France, it's basically the same. Proof of vaccination and a filled out France passenger locater form.
Since you are flying BA, Download the "Verifly" app and it will guide you through what you need and allow you to print out your boarding pass before going to the airport.
I fly back to the UK in a couple of days, from France and on BA, and used the app.
Remember... These are the rules as of today, they could change anytime.