[jambop]

This is a complete out of left field idea but could it be a virus and possibly the new virus that has hit some tomato growers in the UK and Europe? The fruit do look not exactly the same as some photographs I have seen of fruits affected by TOBRFV  but then again not very dissimilar especially the fruit shown in picture d . I do suspect that the degree of the extent of the damage to the fruits will vary to some extent so it could be difficult to make a definite identification as I have viewed lots of photographs and all are quite different in the way the fruit has been affected. As I say an outside idea. Some of the photos in this link look not that unlike the ones provided by the OP although the OP does say the plants appear normal.

   ahdb.org.uk/tomato-brown-rugose-fruit-virus-pictures

[Subversive_plot]

The following link provides information specifically on blossom end rot:
https://www.canr.msu.edu/resources/blossom_end_rot_tip_sheet

The damage on AnneB's tomatoes may be related to BER, or may be something completely different from BER. The damage may or may not have anything to do with calcium or another mineral.  It is one possibility.  Since AnneB is providing consistent water, and the plants otherwise look good, nutrients should be moving into the plant tissues.  Since there is no clear physiological problem, deficiencies in soil remain a possibility. 

AnneB, I am unfamiliar with the UK's equivalent of the Agricultural Extension system in the USA (that link shows an example).  I would bet that there is a program similar in the UK.  I suggest that you send them your photos.  I am curious regarding what you find out.  Good luck, I hope you find an answer.

[AnneB]

Well, it seems applying seaweed feed did the trick.   Later tomatoes on Purple Ukraine, Greek and a couple of others are now unaffected.
I have concluded that the Dalefoot compost is fine without feed for smaller cherry tomatoes, but does not last so well with big beefsteaks.  I have to admit though, that one of the beefsteaks, Mr. Novak, was completely unaffected, but he is getting a feed too from now on.