Have tried Mp3Tag and it seems to do what I want.
One oddity though.
I changed some of the tags via Windows Explorer / Properties.
As I had to go out for 2 hours I left the task part done pending my return.
When I got back I found that some of the changes I'd done, but only some, had disappeared and the tags reverted to their previous values.
Similarly when using Mp3Tag I changed tags for the 20 tracks on a CD. Went to the next volume and changed tags as necessary. A few minutes later I went back to the CDs I'd already done to find some of the tags had reverted!
I then thought that perhaps I should Save (Ctrl+S) the changed tags in Mp3Tag so I changed them again and did Ctrl+a and Ctrl+S. Checking them a few minutes later I still found that some tags had reverted.
It seems to have taken 2 or 3 goes at changing them to get the changes to stay permanent.
One final though associated question. When WMP plays a track it shows in top left of the visualisation window the track name alternating every few seconds with the Artist Name and the Album Title. The problem is that the Artist Name seems to be taken from the Album Artist tag rather than the Artist tag. So for a compilation album of, say 1960s music, the Artist Name is always Various Artists, rather than the artist for the current track. While clearly I can change the Album Artist tag for all the tracks is it possible to get WMP to use the Artist tag rather than the Album Artist?
Or have I misunderstood the two 'artist' tags?