O.K. it's been a few days since I was able to get back to this problem, but managed to have another look at it today.
First off I removed the oil filter and the filter adaptor to inspect the oil filter check valve, guess what no check valve???
who informed me that they weren't fitted from 08....on, so re-assembled with new, pre filled, oil filter, I have been half suspecting the oil filter may be the problem all along, and although it was a Buell oem filter from Riders, but I guess there's always a chance there may have been a problem with it, so I decided to fit a new one to eliminate that possibility.?
Next I removed the pressure relief valve again to give it another look see, and on examining it closely I notice a small rub mark on the side of the tapered slide, hardly noticeable but it was definitely there, so I dressed it with some very fine wet & dry until it had almost disappeared. I them found a close fit drill bit, taped the end with a round of masking tape to make the drill a snug fit in the slide, ran the drill at high speed whilst polishing the slide with some solvol-autosol looked pretty good so re-assembled.
Fired her up and after the oil light went out left it tickover for several minutes or until it was pretty much up to normal operating temperature and the oil light didn't come on once in that time, so keeping my fingers crossed that I have cured it
In conclusion assuming I have cured the problem I'm unsure if it could have been the filter, or the pressure relief valve although it didn't appear to be stuck when I removed it.
By the way I used a K&N oil filter the second time around.