It could be Brian, also if you've only used peat and sand there probably isn't enough nutrients for them, I 'm also wondering if you stood them on gravel trays it may stop waterlogged soil and also give a humid atmosphere around the plants, misting can help to prevent a dry atmosphere if the weather is hot ( as it is here at the moment)
I can't see properly, are they cordons, if so they will need the side shoots removing and eventually after 4/5 trusses stopping
I always use bought compost or grobags and have never mixed my own so i can only give you ideas as to the problem, hope it helps

Good advice from Pam, over watering, not enough feed. Let them almost dry out, then feed with Tomarite, let the leaves die off in their own time. When watering are you using hard tap water? use tepid water preferably rain water.

probably needs a boost of tomato feed

thanks for all the answers .im thinking ack when i filled the pots with sand and peat and i put newspaper inside the pop as there are big holes in the pot and it stopped the peat and sand from coming out.it should not cause waterlogging ?im not sure.ive given some tomatorite today .says on bottle once every 5 days so they have has one feed.im watering when the top of the medium feels dry with tap water.,no access to tepid water im afraid.
ive noticed that some of the trusses the heads of the flowers just break off (not on all of them).thanks for the help will keep updated.
brian

Fill your watering can with tap water add a few drops of Tomarite, leave in the greenhouse for 24 hrs. this will be tepid, water your tomatoes in the morning, refill the can for next day. If no watering is required leave in the greenhouse until required.

thanks for all the answers about the tomato leaves going yellow.ive given a feed of tomatorite and although the color has not changed back to green over the last few weeks they continue to grow and tomatoes are forming.ive put it down to placing newspaper in the pot to stop the compost falling through and im thinking that its getting water logged at the roots akin to too much water.tomatorite helped as well.
thanks all brian