How to open/disconnect Perma Plug

[corrideo]

Hi I have a weatherproof set of Xmas tree lights left outdoors, to put them up a "spark" took off the plastic moulded (two pin) plus, poked the wire thru a convenient hole in a wall, reconnected the plug and presto! I want to take them down but he's not available. It'll cost �25 for another electrician, surely I can do it? The plug is hard moulded rubber/resin/plastic with a single recessed screw head, but this just turns and turns when I try to unscrew it. There is a sort of dint the other side - is this important? Help!

[sddsddean]

If the screw won't come out,it might have stripped the thread inside the moulding. Easiest way out of this is 1) Unplug the lights. 2) With a pair of pliers, cut through the wire by the plug 3) Throw plug away (remembering to buy a new one for next year!) 4) Pull wire back through hole and put lights in loft (or where ever). A new plug will be  a lot cheaper than �25.