Sounds like blight to me in which case you need to either burn the plants or put into your wheelie bin, not your compost bin. If they are in containers in the greenhouse put all the soil/compost in the wheelie bin too. If out doors do not plant tomatoes or anything else from the solanum family in that ground for at least 4 years, preferably more.

Definitely blight, which seems to effect plants that are not sheltered from the rain, as it is a rain bourne disease. Best to shelter them in future years, but having said that my father experienced it in his green house last year, we think it came froman open window dripping on the plant. It spreads to other plants quite readily so be careful. Try gowing a variety next time that is blight tolerant.

I associate blight more with toms. grown in greenhouses than out door ones. When there isn't sufficient movement of air through the space. The door to our greenhouse is never closed and Bulba. took two panes of glass from the other end so the air flows through all t he time. Weather not good enough to grow out doors up here.