Bad toms

This sounds like Blossom end rot. This is caused by a shortage of calcium. Difficult to treat as you need to do this before the plants are planted. Are they in the soil, plant pots or Growing bags?

It can also be the result of erratic watering.

They are in very large flower tubs. I mixed some well rotted horse manure and also some bonemeal into the compost (which came from the garden centre.) I thought the bought stuff would not be good enough to feed them for the time it would take for them to produce toms. Thanks for your help though. Could I mix into the top of the soil some crushed and microwaved egg shells ? (I think that must be calcium)
I have kept them well watered on a daily basis.

Are you feeding you Toms with Tomato feed? That may well help. As Spritz says, it could be watering, it could also be the odd weather we are having. The only way to combat calcium deiciency in growing plants is to spray the fruits with a mild solution of calcium, but that is really only an option for professional growers.
Next season, if you are going to make your own growing medium like that, add a little lime to it as well, though the bonemeal should have helped. It contains calcium.

Thankyou for your help.Luckilly I have other tom plants outdoors that seem to be thriving,so we shall be able to have some pleasure from my own home grown stuff.