[rcf100]

Please could you tell me what may be causing this, and if it may spread to all my other tom plants in the green house please.  Only seems to have appeared in the last couple of days

[daisy1990]

looks like scorch to me, is it in a greenhouse? If so have you got water on the leaves? If you cut off the damaged leaves it should be OK

[rcf100]

It is in the greenhouse and I most certainely will have got water on the leaves.  What's scorch? 

[Oliveview]

When water gets on the plants and then the sun gets on them and the water warms and scorches the plants.  We get that problem here outside in the summer.

Pamela

[rcf100]

Sun, are you having a laugh.  Lol, it is the closest leaf to the best sun direction, so could be that

[DD.]

looks like scorch to me, is it in a greenhouse? If so have you got water on the leaves? If you cut off the damaged leaves it should be OK

Why cut it off? It's not diseased, the green bit's still working OK & making food for the plant.