You need to flip this to see why this should be so. Technically, under the Consumer Rights Acts, products can be returned only if they fail be meet one or more of three criteria:
Satisfactory quality Goods shouldn't be faulty or damaged when you receive them. You should ask yourself what a reasonable person would consider satisfactory for the goods in question. For example, bargain-bucket products won't be held to as high standards as luxury goods.
Fit for purpose The goods should be fit for the purpose they are supplied for, as well as any specific purpose you made known to the retailer before you agreed to buy the goods.
As described The goods supplied must match any description given to you, or any models or samples shown to you at the time of purchase.
No quibble returns grew out of the mail order business and now extend to most retailers but it is, essentially, a concession.
Clothes are a special case for obvious reasons. They need to fit. As we know, manufacturers sizes vary greatly so it takes account of those variations.
The M&S easy returns policy was once remarkable and many people will have favoured the store for that reason.
Despite the general no return policy regarding bedding for reasons of hygiene, there may be a fall back under the third category. If the product has been described as, say, a luxury fabric and is actually flimsy poly-cotton or the colour is more purple that pale blue or in any way does not match the retailer’s description, you should be able to return it butr make your reasons clear - that it is not as described. If it is as described and you just don't like it you won't have any grounds.
Your options:
You have the right to reject your item and get a refund within 30 days of possessing the goods.
You could also ask the retailer to repair or replace your item within six months of purchase.
Your rights against the retailer can last for up to six years, but after the first six months the onus is on you to prove a fault was present at the time you took ownership of the goods.
You can also use your guarantee or warranty if your product develops a fault.
(Source: Which)