Posted: 15/06/2014 at 15:36
David, how are they curling? If the leaves are rolling in from the sides to the middle, so that the underneath surface of the leaf is showing, that is likely to be due to overwatering. If this could be the case cut back on the watering and it should resolve.
If the leaves are curling downwards and the under-surface isn't showing, then that could be due to variations in night and day time temperatures, draughts, or sometimes it's just a tendency of the variety.
There are lots of threads on here about tomatoes; just put tomatoes into the search facility and you'll get loads of information, but if you can't find what you need or it doesn't make sense to you, just ask