Had a bit of a breakthrough!!!!
Remembered I had an ooooollllllddddddd PC from around 1999 in the loft, got that out had a look at it's PSU, it is 245W, same make as my 450W PSU but with only a 20 pin main power connector instead of a 20+4 pin connector along with a 4 pin extra power connector. Anyway connected this 245W PSU to my new build even though it only had a 20 pin connector, and it burst into life first time!!!! it beeped, fan went round like a proper working PC!! (sorry getting delirious now

)
I said that I was talking myself into a new PSU, think I've just confirmed it!?!?!?!
How does this PSU look to everone?
http://www.overclockers.co.uk/showproduct.php?prodid=CA-059-CS&tool=5