Amazon is an authorised on-line dealer of Canon products, however many of the Amazon Market place sellers don't seem to be listed by Canon as being official dealers.
This means that whilst I can assume lenses sold directly from Amazon are legitimate Canon UK stock and therefore carry a valid manufacturers warranty, there is no clarification as to whether other Market Place sellers are selling imported or UK stock.
I have written to both Amazon and Canon for clarification about this point, but neither have bothered to reply.
So when is a lens sold through an authorised dealer actually a grey import? You decide!