"Do you accept that I am a truthful person?"
"Then, as a truthful person, I am telling you that I bought these defective goods from this branch on 17 October 2016 for £20.16 and paid cash."
"I am sorry sir, but company policy is that we must have a receipt."
"Then company policy is wrong and silly. Do you really want me to leave the goods here, go away, issue a county court claim on line and ask the court to award me £20.16, interest on that sum from 17 October 2016 until I obtain judgment at the rate of 8%, my travelling and out of pocket expenses for coming in today and any expenses for trying to source replacement goods plus interest and court fees? Such a waste."
"Could you just hold in and I'll talk to my manager?"
I have had that conversation. It has done the trick. If there is nothing wrong with the goods and you are seeking to take advantage of the shop's scheme for return simply because you have changed your mind or your spouse has told you that you look hideous in the jacket, then you have to play according to the shop's rules. And if they say that a receipt is required for a refund, exchange or credit note then a receipt you must produce.
But if the goods are not up to legal standard and you are entitled to a refund then it is reasonable enough that you satisfy the shop you did not buy the goods from their ace rivals two doors away. Perhaps you have a credit card statement. But there is no law that you must come up with the receipt which you have probably screwed up and thrown out of a bus window (that was naughty) before you get your money back. If written evidence of purchase is just not available then you are still entitled to a refund. If you sue for it and the judge is satisfied it is more probable that not that you are telling the truth, you will win.