It may vary from area to area, but at least some areas have transport ambulances, that have a couch, a place to lock a wheelchair so that a person in a wheelchair can be transported while in the wheelchair, and some seats, like a third of a minibus. They go round and pick people up and return them home and see them into their home, either for an outpatient appointment or for inpatient treatment. The transport ambulances are different from the "blue light" ambulances that have a couch and lots of medical equipment.
Booking is by contacting the Patient Transport Service at the hospital.