What does “middle class” mean in the UK?

I’m watching a show on BritBox “Murder in the Village” and they keep referring to this couple (he’s a doctor she was a social worker) as “middle class”, followed by “wealthy”.

In the US, middle class is not wealthy but a family that has all their basic needs met comfortably with a bit extra for a holiday or a few nicer things. It’s confusing to see middle class and wealthy in the same context. Could someone enlighten me please? Thanks so much.