Game Pass Ultimate - £1 (Convert old subscriptions to Ultimate) - Xbox Store

CDKeys seem to be sending out used XBL Gold keys at the moment - avoid!
Cheapest I could find was Instant Gaming (£37.22) and I can confirm that the code worked.

If you have recurring billing switched off before you redeem the code, you can get a bonus month by allowing MS to switch it back on

All the questions that you guys may have is answered here:
xbox.com/en-…ass

The maximum subscription you can extend to is 36 months. So for best deal your Xbox Live+Game pass subscription (and/or combined) should be around 36 months. Say for example you have 21 months of Xbox live and 10 months of game pass left, then to get the best deal you should extend your live subscription by 36-21-10=5 months before getting this deal. If you have say only 13 months of Xbox live and no game pass, then you extend by 36-13-0=23 months before getting this deal. It is not necessary or required to extend to 36 months but this give you the best value for money. Hope this helps.

Another option for 12 Month Xbox Live subscription is Electronic First at £39.49 currently (Some places popping prices up Link HERE