I used to work in a returns office at John Lewis and you have quite good rights on your side.
You have 7 days to advise them by letter, fax or email. The seven days is the seventh working day after the day on which you receive your goods. (So if you received it on a Monday, you have until the following Tuesday).
You must also, unless stated otherwise in the agreement, make the item AVAILABLE for collection. You are not obligated to pay to send the item back (though you may with to do so for a smoother running return process). It may state in your contract, or 'terms of sale', that you must foot the price of any returns. Upon receipt of the cancellation of your contract the retailer has 30 days to refund your money.
Any damage to packaging or contents, or any missing components may void you right of cancellation.
All this should be covered on the OFT website or the Consumer Direct website in some detail.
Hope this helps.
(P.S. Take the batteries out of the remote control and place them in a suitable plastic wrapper, or at least break the circuit in the remote with a piece of paper/plastic. This will ensure they don't leak.)