I think
this short article on the history of dubstep has some good information.
That article mentions a 2002 cover story in XLR8R magazine which was actually an article on Horsepower Productions - the cover has a photo of HP with the word 'Dubstep' in large lettering and a subtitle "an inside look at London's Dub 2-Step." I still have a copy of the issue and have tried to find any of its articles online to link here whenever this topic comes up, but I can't even find an image of the cover.
edit: I just checked myself and the full title of the cover story looks like this
"Feel the power! It's...DUBSTEP; an inside look at London's Dub 2-Step Underground with Horsepower Productions, Ammunition, EL-B, Jason Kaye, Heartless Crew and more!"