Purism stuff
@Shrigglepuss the bit of law to look at is The Consumer Contracts (Information, Cancellation and Additional Charges) Regulations 2013
http://www.legislation.gov.uk/uksi/2013/3134/contents/made
If you inform them of your intention to cancel the order in writing by fax or email then they've got 14 days to refund your money before they're in contravention of it, there's a form letter to do that in schedule 3