The distraught mother of 29-year-old Anita Chalmers called in the police when her daughter failed to arrive home at Tilehurst, Berkshire, from a training centre in Reading.
It took officers three hours to find the Down's syndrome sufferer huddled in the back of a council social services bus, parked in a depot in Reading. The driver thought he had completed his round and had gone home for the weekend.
A Berkshire County Council spokesman said: 'We very much regret that this has happened . . . the driver concerned has been dismissed.'