Just to update the situation for people here as I received so much assistance from you.
I returned the faulty PSU on March 9th and my replacement arrived last Monday [21st]. This was a little longer than I would have liked. While I used the basic registered postal system and was notified that EVGA received the package in the UK less than 48 hours after posting, EVGA used UPS to return which took 5 working days to get back to me. What was worse is EVGA supplied an incorrect tracking number with which I was unable to track the return, necessitating altering household schedules so that someone could be home in the 'hope' that it would arrive. Nevertheless in the end I was just glad to be able to get my game on again when I did get it so...
The replacement PSU was as one would expect, a refurbished unit which I'm OK with as in my limited experience, refurbished have worked fine for what I would expect a component's life to be. However that opinion is forever changed as of 11AM this morning when I switched on the PC and ------ nothing.
A click registered when I pressed the machine on and both the motherboard and GPU lights flashed on for a moment. The water pump and the fans whirred on for less than a second but went dark and silent again then and the PC would not come on, even post.
As before, I swapped out the EVGA PSU for an old Seasonic 500W PSU for just the CPU and Motherboard power and PC came on as normal. I refit the EVGA one again with just the CPU and Motherboard power and nothing. So after 4 days of use, the replacement unit died.
The cost of me RMAing yet another registered/insured 2.25KG package to the UK would mean that I would in essence be spending more than a third what the bloody thing cost me originally to potentially get a third dud!!! So I think it's pointless going through the RMA process again at this point "Fool me once..." and all that, so I went off and got a Corsair PSU instead to put the machine back into working order.