My subscription is now good until Dec 2015!
- Buy a £35 PSN card for £29.99 - http://www.cdkeys.com/playstation-network-psn/psn-cards/playstation-network-card-35-ps-vita-ps3
- Go to the PSN store and add that to your account wallet - http://store.sonyentertainmentnetwork.com
- Add a 1-year subscription, which until Sept 20th 2013 will include an additional 90 days - https://store.sonyentertainmentnetwork.com/#!/en-gb/reward_game/playstationplus-one-year-subscription*/cid=IP9102-NPIA90006_01-PSPLUSSUBS365DAY
- Checkout, which will require an additional £5 top-up, can be done here.