The park is full of ripening blackberries, all free from the contaminants of vehicle exhaust. Here is a recipe for blackberry and apple jam.
It suggests using frozen blackberries so that you can make jam at any time of year, but it works even better with fresh blackberries. Try it.
UPDATE: there are apple trees on council land around Trowbridge of which the council says, “people are welcome to collect windfall apples in public open spaces.”
So. . . . pick your blackberries in the park and your apples from the big roundabout on Bradley Road.