Thank you all for your thoughts on Passata etc, Think I'll still trundle on as usual. I can't imagine being so dedicated as to eat tomatoes straight from the tin.
I was given a very useful tip by a fellow gardener a few years ago who saves her own tomato seed.Scoop some fresh seed onto a piece of kitchen paper, keep it out to dry completely, then label it and put it in a bag in the 'fridge until the appropriate time. Put the piece of impregnated paper straight into a pot of compost then prick out the seedlings in the usual way. It works well with home grown tomatoes or bought ones. You don't get F1 hybrids this way of course and I hope I'm not doing the seed people out of too much money but it is a big saving. Happy munching.