Hard to say but it does look like blight to me. Some brown concentric rings surrounded by yellow. Doesn't always get the fuzzy spores on underside. If I cut off affected leaves/stems and spray Neem oil after- it's pretty much under control for couple weeks. I do take out a rag with a bit of bleach/water on it to clean knife between cuttings.

Thank you for your suggestion. I have ordered some neem oil for tomorrow so fingers crossed it should work. I think we overcrowded the greenhouse a bit and with the damp weather was a bad combination. Oh well, live and learn :) Thank you again so much for your help.

I agree that the likeliest candidate is early blight. Prune affected foliage. I prefer copper to neem, but there are many options and the decision on what to use is personal.