Many thanks for the contributions so far.
The range I found this on is almost only used by the British military. They take a few civilian bookings but these are often cancelled if an 'official' need arises. Thus far I've not seen this ammunition for sale on the surplus market here in the UK, is there any chance that this was being used as GPMG fodder?
It would seem that the stores are being emptied of the GPMG and that they are being bolted onto anything and everything in both Iraq and Afghanistan. Given that they serve to keep the other fellows heads below the parapet I wouldn't suppose quality of ammunition was a prime consideration as long as sufficient training had been given in clearing stoppages.