Tesco currently have these on offer at £1
However if you print off this voucher (FB like required) you can get £1 off the price, meaning you get this for FREE
Like page, click my account and print off £1 voucher.
Please note if you've ever printed of a voucher from this page before you won't be able to again!
Pressing 'Try Again' also prints out another voucher.
Hope this helps.
EDIT: Recommend going to normal checkouts with these.