The supermarket Asda have this scheme where they say that they will be 10% cheaper than other supermarkets or they will refun the difference.
So I have done this a few times and I have had money off vouchers ranging from 80p to £5
I think this is really good.
All you have to do is enter a few details from your last shopping receipt on to there website which I will link here. You can them print out your voucher and take it to the store when you do your next shop along with your old receipt. You do need to take both the voucher and the old receipt.
Today I did mine from the receipt from just before Christmas and I got this
There is only one down fall you have to use the voucher withing a few days so I would suggest doing it the day before or the day that you are going shopping.
Not sure how long that they will keep this scheme going but I think it’s fab.