Hi again Chumba Wumba - The reason I suggested the Slow Worm is from your description and also the length. They also shed their skins - and like coastal areas.
There are only 3 snakes in the UK, Adder, Grass Snake and Smooth Snake. Now the Adder is distinctive and 18in to 2ft in length - so that's out. The Grass Snake is 2-3ft long, olive brown with vertical black bars along each flank. The Smooth Snake is 18-20ins - but is only found in Dorset, Hampshire, Wiltshire, Surrey and Sussex.
All this info has been taken from about 3 different ID books, so it's been checked....but I'm totally baffled because everything(except the tongue) still points to the Slow Worm.
Perhaps you could take a pic of your 'visitor'and show it to a reptile specialist - (the proper title escapes me at the moment!) I'd love to know when you have the answer.