I'll be honest here and admit that I don't know much about Zealot. In fact, apart from their hometown Leicester, Zealot are complete strangers to me. Their demo was on the other side of the Dreadful demo tape and I only have the tracklists. No cover, no recording information, nothing and I couldn't find anything about Zealot on the web. Now, that's an obscure catch, isn't it?
Judging from the music it is safe to assume Zealot were from the mid-late 80's (1987 seems like a relevant guess as far as this demo is concerned) and they were rooted in the anarcho side of things (they do have an anti-hunting/animal right number and a song called "Double standards" about sexism). However, they don't really sound like your typical English band from the period. I guess they listened to a quite a bit of US hardcore and crossover. I suppose the most appropriate comparisons would include Rhetoric and early Concrete Sox but also Septic Death or even a far less metallic Energetic Krusher. It is really fast hardcore punk with distinctive mid-tempo thrashy breaks and angry vocals that remind me of Debauchery or even Deviated Instinct. The singer really sounds pissed off and threatening but the real stand-out of the tape is the addition of a female singer on a couple of songs with a great haunting voice not unlike Post-Mortem or Violators singer's. In fact, with this in mind could almost say that if The Mad Are Sane, Toxic Waste or Symbol of Freedom had gone thrash they would sounded something like Zealot. Finally, the sound is rough but you can actually hear all the instruments which is not a quality you can find on all recordings of that era (oh well, DIY or die as they say). I really wish I knew more about Zealot because I have the feeling those fellows might have been on to some other bands than this one.