No idea how valid this is, but at least one source gives today as the date this demo was "released" in 1983. Sold by the band through zines, tape trading etc. Known as What Lies Ahead, the demo was a collection of rehearsals and live recordings.
Anyway, a chance to remember the punk roots of ONSLAUGHT: DISCHARGE, GBH, EXPLOITED all clear comparisons. Despite the image and lyrical changes on the first album Power From Hell, ONSLAUGHT continued the sound you hear on this demo. Getting faster and heavier in the way bands like BROKEN BONES were around the same time.
Early ONSLAUGHT is killer, and they continued to kill as they became the black thrash cult heard on The Force with new vocalist Sy Keeler. Throughout that period Nige Rockett on guitar and Steve Grice on drums.