Just been to Tesco in Watford to get Despicable Me which is released on Dvd today. They are offering it for £12 or £7 if you spend £40 instore.
The till isn't deducting the £5 when you spend £40 so a quick trip to customer services gets you double the difference refund of £10!
So check your receipt if you've already been this morning or go quickly if you want to get it. The customer services lady said they were aware of the problem so I don't know how long it will be before the error is corrected.