Posted: 12/07/2013 at 18:27
Thanks for your reply Italophile! Useful information to have. I wondered about a deficiency. They're in commercial multipurpose compost and have had 2 doses of liquid feed - the first a cheap commercial tomato food, the second seaweed extract in case the tomato food was lacking anything.
Unfortunately I have now snipped the discoloured leaves and don't have any more pics. A lot of the tips on the outside ones (2nd photo) were also black and shrivelled. The ones in the little green house weren't as bad as I thought at the top.