Traditionally so did many schools (sports fixtures were then usually on a Weds afternoon). A few still do this.

I know some GP practices that still do this (quite astounding given the current issues in the NHS).

I actually think it's quite astounding that they haven't been forced to give this up, and I hope they never have to.

Specifically, when I go to my GP, the staff are always busy, don't appear to get much of a break at all. I doubt a half day on a Wednesday makes up for extra hours put into their job just to get through the week.

I mean to me it makes sense that they would be less busy if they worked a full week like everyone else. When we have a shortage of GP's and it's impacting people across the country (and having a knock on effect on hospital A&E usage) disallowing 4.5 day weeks would probably help. There are obviously much bigger issues at play (e.g. recruiting GP's) but that doesn't mean we should ignore things that could impact immediately in a smaller way.

The odd thing is that you have about as many GPs per capita as Norway yet GPs in Norway don't seem to be anything like as busy and they are also much easier to get appointments with. I do realize this is anecdotal evidence though.

I think it would likely increase the exodus of GPs and exacerbate the problem rather than ease it.