I can't speak to UK airports but TSA policy is that any medication needs to be in the original container, including prescription medication. So if you have any unmarked pills they'll toss them if they find them, same with multiple different pills in a prescription pill bottle or similar.
Never encountered that over probably hundreds of flights. From what I read, it's recommended but not required. I'd probably be more conservative with any controlled substances. (And, based on some things I've read, it's probably not a bad idea to have a photo of the labels.)
I mean it was the truth. It was legitimately prescription medication. In this case. But I can imagine someone could lie.