ermintrude35 may work for a consumer-friendly retailer but the policy which they employ is not in any way standard. There is no legislation which entitles consumers to a refund if that consumer "changes their mind".
Statutory rights to a refund exist wherever goods do not "conform to contract". This means they must be as described, fit for purpose and of satisfactory quality (i.e. not inherently faulty at the time of sale).
If goods do not conform to contract at the time of sale, purchasers can request their money back "within a reasonable time". (This is not defined and will depend on circumstances).
http://www.dti.gov.uk/consumers/fact-sheets/pa ge38311.html
Retailers offering more than this statutory minimum do so as a gesture of goodwill.