These tomatoes don't look very healthy!

For thirty years I've successfully grown three bush tomatoes in a growbag similar to the photos. Now, for the first time, these appear to have suddenly become poorly with wilting and dying leaves. I've never seen blight, but this doesn't look like it from photos I've seen. What do you think?

 

Not blight, that causes brown patches. Looks as though they are hungry. Could it be because the grow bags are peat free instead of the old sort of peat based ones? You could try watering them with a liquid tomato feed.

 

I'd suggest maybe magnesium deficiency, but nothing drastic.
Either too wet or too dry.

 

I think that is a magnesium deficiency. Can be due to excess potash in feeding .Made worse by cold conditions.
Buy Epsom salts from Boots. Use 1 teaspoon per litre of water, dissolve and apply with fine sprayer to lower leaves in the morning. Allow to dry by ventilation.

 

Thanks all, will get Epsom Salts and make sure I'm watering properly. Would be surprising, but could just be the latter.