Not posting this as a voucher, as we don't actually have a voucher code, but posting as a tip to let people know about the deal. If you buy this month's company magazine, there is a unique code in it, which will give you a 20% discount code for asos, when you register at getlippy.com. There has been news of this for a week or two, but getlippy have just arranged the box for their code on the site.
If you haven't registered, go to getlippy.com and do so. If you are already a member there, just log in, and you'll see the box for the unique code. They'll email the 20% asos code right away :)