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Hi, In this damp weather it could well be blight. There is no treatment for blight, it's only possible to treat plant to prevent blight.
When you are sure it's blight, dig them up and burn them.
For next year, definitely don't grow tomatoes (or potatoes) on the same piece of land for 3 years. Spray with bordeaux or whatever else you prefer to use, in early to mid June.
Comiserations for this year.