553.1.5 A plug and socket-outlet not complying with BS 1363, BS 546, BS 196 or BS EN 60309-2, may be used in single-phase a.c. or two-wire d.c. circuits operating at a nominal voltage not exceeding 250 volts for:

( i ) the connection of an electric clock, provided that the plug and socket-outlet are designed specifically for that purpose, and that each plug incorporates a fuse of rating not exceeding 3 amperes complying with BS 646 or BS 1362 as appropriate

( ii ) the connection of an electric shaver, provided that the socket-outlet is either incorporated in a shaver supply unit complying with BS EN 61558-2-5 or, in a room other than a bathroom, is a type complying with BS 4573

( iii ) a circuit having special characteristics such that danger would otherwise arise or it is necessary to distinguish the function of that circuit.