Public surface water sewers
These drainage systems cater for rain water running off the surface of areas of hard standing and other generally impermeable areas such as car parks, industrial land and public amenity areas, and from the roofs of buildings. Responsibility for them is vested in the sewerage undertaker (usually the water company). Public surface water sewers are recorded on a map of public sewers held by the sewerage undertaker.
You should contact your local water authority for further information.