I had a feeling they wouldn't be too happy about you wanting to return anything.
If you've had the item for less than 7
working days from receipt of the goods then you can return the item under the Distance Selling Regulations and all you would be required to pay would be the post&packing back to them (which would be cheaper than the 30%). There are certain excepts and the goods have to go back to them in as new a condition as possible. See
this site and the FAQ's and then if you want ring your local trading standards for advice.
UPDATE:
If you are within 7 working days then you have to write to them and/or email them with your intentions of returning the item under this regulation.