Thanks for all you comments, seemed I've started a big debate.
I somehow managed to mislay this post so here is it again - apologies if it turns up twice.
I've tried that but he won't even return my calls - so I need to take it to the next level, whatever that may be
Theres no chance of...
In Dec 2004 we had a new hot water cylinder installed by a corgi reg plumber. In Sept 2005 we noticed a very slight leak coming from the seal where the immersion fits in - we can feel its wet with our fingers, and occasionally there is water sitting under the cylinder which has run down the side...