Its "black bottom"

Blossom end rot,

Put that in the white search box at the top right, theres pages on Goy about it.
Basically its caused by uneven watering, the hot weather, a chemical imbalance and even the variety.
Hopefully those pages will help you to learn what to do......and realise its not just you getting it :0)

I have grown 4 Gardener's Delightplants, and 3 other kinds but none of them are as good as past years. I've done nothing different - but they're all smallerand not so numerous. Not sure what to blame for this setback.

I blame everything on the weather!

But saying that I bought bigger grobags this year, and one ordinary one.....the offer was for 5 and I needed 6
the one in the smaller cheaper bag are paler and the toms less and smaller.
The ones in the bigger bags are much better, after last year these are so sweet and juicy, I,ve been picking the cherry ones since july and the bigger since the beginning of this month.
So different from last year, the sun has much to do with that, here it was grey all last summer and although the toms ripened the taste was poor