Instructions:I had this through the post and it said it was because I haven't ordered anything before, so I guess it only applies to new customers (though if a current customer could try and let us know?).
Word of warning though - the mail shot said it excluded electrical items between certain pages, and what I wanted to order was outside of the pages. I called to check, they said it would be ok, and when I rang back after placing the order they told me it wasn't applicable to even MORE pages - which were in the small print, and now DID include my item! It also claimed i had to use the offer within 8 days, but thats hardly ever true either!
On principal I doubt I'll use this myself (I cancelled, even though they said I could however have 20% off using ZJ12) but maybe someone else would like to get revenge for me and go crazy with it!