This is blossom end rot, your soil medium in which they are planted has no grit or sharp sand, hence wet condition at root level. A drastic measure is to lift your plants with a large fork for about 2 inches up from their present level, continue to water in the morning at the same rate as now. Ventilate day and night if in a greenhouse.

Thanks Doctorbog 1 The only problem is the plants are in pots in the greenhouse and are now about five feet high Is there any other way round this. Sorry to sound naive but i am fairly new to greenhouse keeping

Sorry for the delay in answering Silverrow, I've been away for the weekend. Raise the pots up with pieces of roof tile underneath. As I said vent day and night. Stop at 5 trusses, keep taking off side shoots. Next year you may like to try ring culture.

Thanks for getting back to me Doctorbob 1.I have taken your advice and am watering morning and evening also leaving the door slightly open through the day. I have lifted the pots about two inches of the ground as you suggested.Fingers crossed the rest of the crop will be ok. Thanks again for your advice. Silverrow

You're very welcome Silverrow, good luck with the rest of the crop.