Play.com have this for £10.99 which is a hot deal in itself but using PC World's price match promise this can be had for £8.79.
Bring the play.com page up on your mobile while in store or print a copy of their price promise and the play.com page and go to a PC World store.
Pick up the card and go to checkout.
Present the page to the checkout operator and ask them (nicely) if they can price match this for you.
Make sure they deduct 110% of the price difference and not 100% (£24.2 and not £22)
You should pay no more than £8.79 for this card.
I have done price matches at various PC World stores and never had any problems.