Tomato problem???

I agree, they can look very similar FP, botrytis and later blight. However, if it is just one outside plant at the moment, I would assume it to be botrytis.
These last 3 or 4 years I have planted outside tomatoes with leftover seedlings more out of an afterthought than expectation. I'm almost expecting them to be taken by blight before the end of August.
Indoor ones are quite a different matter as there are options.
When blight comes to our site, which it probably will, the choice is does one shut the greenhouse door and encourage botrytis or does one keep it open with the threat of blight blowing in... at least with the door open it is more likely there will be no moisture on the leaf and stem surfaces.
And from experience, at least botrytis can be contained, managed and a reasonable crop obtained in a greenhouse with blight outside. A tough call.

Medwyn suggests lemon juice as a treatment, which may work - although - it's illegal to use it according to the EU.

I find it very hard to believe that the EU would make the use of lemon juice illegal.
Have you a source for that info?