This is from gov.uk
"Accepting returns and giving refunds: the law
You must offer a full refund if an item is faulty, not as described or doesn’t do what it’s supposed to.
Check when you have to offer refunds and accept returns.
Customers have exactly the same rights to refunds when they buy items in a sale as when they buy them at full price.
When you don’t have to offer a refund
You don’t have to refund a customer if they:
knew an item was faulty when they bought it
damaged an item by trying to repair it themselves or getting someone else to do it (though they may still have the right to a repair, replacement or partial refund)
no longer want an item (eg because it’s the wrong size or colour) unless they bought it without seeing it
You have to offer a refund for certain items only if they’re faulty, such as:
personalised items and custom-made items, eg curtains
perishable items, eg frozen food or flowers
newspapers and magazines
unwrapped CDs, DVDs and computer software
Online, mail and phone order sales
Online, mail and telephone order customers have the right to cancel their order for a limited time even if the goods aren’t faulty. Sales of this kind are known as ‘distance selling’.
You must offer a refund to customers if they’ve told you within 14 days of receiving their goods that they want to cancel. They have another 14 days to return the goods once they’ve told you.
You must refund the customer within 14 days of receiving the goods back. They don’t have to provide a reason.
Repairs and replacements
If a customer has ‘accepted’ an item, but later discovers a fault, you may have to repair or replace it. The customer can still reject the item after it’s been repaired or replaced.
A customer has accepted an item if they’ve:
told you they’ve accepted it (having had enough opportunity to inspect the item before confirming they’ve received it)
altered the item
You must repair or replace an item if a customer returns it within 6 months - unless you can prove it wasn’t faulty when they bought it.
You can ask a customer to prove an item was faulty when they bought it if they ask for a repair or replacement after 6 months.
Customers have up to 6 years to make a claim for an item they’ve bought from you (5 years in Scotland)."