Just found this on MSE.Read carefully maybe a glitch???
THIS IS NOT ADVERTISED IN STORE BUT
Buy a £25 iTunes download card in main Tesco stores and you will only pay £20 for it - effectively giving you £5 extra for free.
How to get it?
This deal is available from customer service branches of Tescos but not online. When you pay for the card the £5 is automatically deducted from the cost. However please read the following important notes:
We have tried and tested this. It was reported to us by a number of MoneySavers and we have been to Tesco (Shepherds Bush branch) and bought one - and the £5 was taken off at the till.
There isn't any instore signage. You won't see signs of this instore or on Tesco website, and many staff don't know about it.