That is, I think blossom end rot. Is no one having any luck with Toms ?

Thank you Pimpernel for your prompt answer. I've looked up the condition and see it's due to low calcium, possibly caused by too much nitrogen; so it may be due to excessive feeding.

Blortwick

yes it is blossom end rot, so ensure that there is no shortage of water remove the damaged fruit and improve the watering,
it can be a lack of calcium so keep the plants waterd and feed every week with a good tomato feed