Play Asia have 12 months for about £29, they will email you the code. Unless anything has changed live gold codes should work on an account from any region, although you might want to double check that. I have used a US gold card on my UK account perfectly fine anyway.
£29 is the cheapest? I remember seeing Amazon UK marketplace selling for around £25. I'll wait for a price drop, not in any way in a hurry to play online.
Cheapest on Amazon looks to be around £34 atm, every so often I have seen it for £25ish, just not recently. I got 12 months of gold for £21 I think it was the end of last year direct from the dashboard, thats the cheapest I have ever seen a 12 month subscription for. Also got a total of an additional 8 months for £8 through the recent Xbox.com / Dashboard offers.