Covid test to return to US...where, how, what is your experience

When I looked into this, I was just going to find the nearest Boots and/or train station pharmacy and have it done

Plenty of places to get them including many pharmacies and the airport. Earlier this month we got ours at the ExpressTest center at Paddington Station. We we able to take our test before our scheduled time, it only took a few minutes, and we received our results in about 30 minutes.

As a side note, with all restrictions having been removed, some testing centers are closing so there may not be as many as before. The center we went to had been testing 1000 people a day, but was down to a couple hundred. There was no line at all.