There are various oddities from mid 90s drum & bass that sound like proto dubstep. Jay Majik did stuff as Innervisions that is really slow and cavernous, like inner city dub - I got
this one and it's great, top record. The drums are hip hoppy though, they don't have the swing. But in terms of atmosphere, it's a dubstep record.
Photek's Into The 90s sounds garage-y if you play it on 45, I knew garage DJs who used to do this.
This UR record is wierdly dubsteppy too - like halfstep techno, quite bleakly ambient.