AN investigation has begun after an important part of a historically significant mill site was destroyed. Low Mill on Gresley Road in Keighley, dates back to 1779, was the first cotton mill to be built in Yorkshire and is one of just two Grade II* listed buildings in the town. The mill was powered by water diverted from the River Worth through a series of sluices a goit. But the building has been derelict for decades, and last year it was added to Save Britain’s Heritage’s “At Risk” register of historic and heritage buildings that face an uncertain future.