I used to use this with my lawn mower. The Residual Current Device (RCD) is a safety cut out device when using power tools eoth a cable that need to be plugged into the mains. Both are in good condition have been kept in inside and are no longer needed. I haven't measured the cable, but it was from B&Q and I am guessing it is a standard 15m. 
Fair Chance Policy: I’ll wait before choosing a recipient to give more people a chance to reply.
 Outdoor extension lead and RCD (Near Lowther Gardens FY8)
Collection Times
Any time with 3hrs notice from 3pm on 31st Oct
  Any time with 3hrs notice from 3pm on 31st Oct
                                This offer has been gifted to someone and is no longer available.