It is quite common for lower leaves to have problems.
How many trusses have you got on your plants?
What do the upper leaves look like?
What are you growing them in?

A lot of tomato problems are a combination of overwatering/underwatering/lack of feeding/extremes of temperatures. Could be any of those.

Thanks for the help. The plant are of a bush kind, that according to the instructions you don't nip anything off. The upper leaves are fine with lots of flowers. They are in large pots. Again according to the instructions I am to start feeding (twice a week) when 1st fruit shows (there are a few at the moment so I was going to start feeding). I THINK I have the watering right and the temperatures seem to be consistent, not any better than cool to mild. Not much sunshine though in the dark and dreary north-east.

Watering in pots is always difficult to guage. If the upper parts of the plant are nice and green and healthy then it sounds as if that isn't the problem. I'd just remove the yellow leaves and if the first truss is a bit dodgey then remove that and hope the others behave themselves. First trusses can also be a bit erratic setting so when you say flowers dying it could be that they just haven't formed the fruit. I'd still start your fertilising now.
I've never grown bush tomatoes before, but are they not usually grown outdoors?

Outdoors? Good point but unfortunately I have'nt got a clue!

If humanly possible, always grow your tomatoes in the soil of the greenhouse bed, enriching it with lots of compost and so on before planting. That will overcome many of your watering problems. Failing that, try ring culture over a deep gravel bed. Unless you are there all day and can water frequently, I've always found a pot or bag culture to be full of problems with soil drying out, blossom end rot, and yellow leaves. Since I started growing in the soil bed I've had no problems even though I've been using the same soil for over ten years. (with lots of additions of compost)