Just tried to add my UK card using my mate's Turkish number for verification. It wouldn't accept the number even though its a valid Turkish one. Then it locked my browser out. So Netflix really are being sneaky. Still the vouchers work for the moment. I do have access to another UK sub for free but its only HD and I do like the UHD on my big TV.
Thanks @spats and @alexanderras for the really useful info on this.
Thanks @spats and @alexanderras for the really useful info on this.