They look much like air- conditioning units and plug into a typical household electrical socket.

The cost of changing an electrical socket, for example, ranged from 30.81 to 302.30 and fitting a new lock could cost anything between 15 and 486, says the report.

You fit a small dynamo on either the front or back wheel and a cable runs from there to an electrical socket bolted either to the crossbar or handlebar.

Hospitals and schools are being fleeced by contractors charging as much as 300 to install an electrical socket and 486 to fit a lock, the public spending watchdog says today.

That would be enough to pay the average handyman to replace a light fitting and an electrical socket, hang a picture, paint a room, and put up a bookshelf.