I've just found this amazing site: Sound maps - Map Your Voice | British Library - Sounds

In fact, I contributed - though I've no idea how anyone could find me. (And geography's no great help, as the map is not as precise as one might wish; it's put Newbury about 5 miles North East of Reading instead of about 10 miles SW. Still, it's close enough for gross accent descriptors (such as 'Yorkshire')).