The bad new- I tried everything you guys suggested and it seems the PSU is dead, can't find the receipt or packaging or remember where I bought it from!
When I built the pc (October 2009) I used primarily Overclockers.co.uk and Scan for the components. This morning I rang both those companies and I didn't buy it from either of them.
In desperation I tried two more UK retail sites with no luck,
Out of desperation I rang CCLonline.co.uk, a company I had thought of using a number of times but didn't think I ever had.
The good news- Bingo, they had indeed sold me the PSU. The guy explained that it was out of their 12 month warranty and would have to be RMAd to Germany.
I explained that I couldn't find a receipt or the packaging. He said, no problem just take it out put it in a box with some bubble wrap and send it back to CCL and they will RMA it for me.
This is going to take about 4 weeks but I was thinking I would just have to take the loss and buy a new PSU.
So a big up for CCL! I really think that's good service. Most companies would have left me arguing on international phone calls to Germany.
Thanks to all of you who took the time to advise me
Still a bummer but it's turned out alright, especially as they no longer make my model and the replacement will have to be a 900 watt unit that's won loads of awards.