Unless an item is faulty, or not 'as described', there's no obligation on a High Street store to exchange or refund goods after purchase. (The law is different to that which applies to online purchases). They're fully entitled to tell you to "go and get knotted" if you try to return a non-faulty (and correctly described) item.
Where a store does, entirely voluntarily, accept returns of such goods, they're entitled to impose whatever restrictions they like upon such a policy. Here's a screencap from Poundland's website:
https://i.postimg.cc/cLTGWnn4/Poundland.jpg