MOS your spot on. BTW the link I posted states just that
If your goods are faulty, or you're sent substitute items that you don't want, the retailer must pay return postage costs
Which links to this section
Returning faulty goods
If you receive faulty goods and wish to return them, The Distance Selling Regulations are in addition to your other legal rights.
So, if your goods are faulty and don???t do what they're supposed to, or don???t match the description given, you have the same consumer rights under the Sale of Goods Act as you have when buying face to face.
Any terms and conditions that say you must cover the cost of returning an item wouldn???t apply where the goods being returned are faulty.