UPDATE:
You're not going to believe this......The chap came out today and found a fracture in the cold return pipe that runs along side the rocker cover then round the back of the engine into a aluminium block then the pipe continues on down to the bulk head. The pipe was fractured at the entry point to the block. He carried out a localised repair at the fracture and also replaced an o-ring on the opposite side. He had it on test for 20 minutes and all was fine. It cost me £130 and off he went. I drove 2 miles home and on the way the cold air stopped flowing and I looked under the bonnet when I got home and found that the seal had blown and now i've got UV dye down the back of the engine bay. BORLLOCKS!!
Anyway, I gave him a call and he's now coming back next Monday and it looks like the whole pipe assembly will have to be replaced. I think the pipe is going to cost around about £170, then there's the labour of about 2 hrs to fit it. In all fairness, he did warn me that this could happen but it still bugs the crap out of me.
cryb..