No need to be worried about being conned by websites claiming cheap xbox live codes.
Many users will receive a message on their dashboard, you may have to purchase the 1 month for £1 deal first.
£2.67 a month (based on 12 months at £31.99)
With a years subscription going up to £45. If your membership doesn't run out for another few months you can sign up for this and it will be added to your account. So when it does you will automatically go onto this.