what is happening with our tomatoes

Its blight. Bin or burn all foliage at end of season including roots and rotten fruit. The wet and humi dweather causes it and the rain will splash it onto any unaffected plants inc spuds.
Bin and burn all leaves and rotten fruit that fall off or you remove.

Yup sadly no solution now but to destroy. Remember not to plant tomatoes or potatoes where the tomatoes were this year as the spores can, and do, live on in the soil. Also when Nicky says 'bin' he means exactly that do not put any of the plants anywhere near your compost bin!