Regarding ANGEL WITCH and without looking any of this s**t up but from memory Kevin Heybourne guitar/vocals/song writer was the main guy in the 3-piece and the ANGEL WITCH drummer had a sister who was the drummer in GIRLSCHOOL around the same time 1980. Later on in the 1990s I think the band may have become a 4-piece band and switched musical styles to a more blues/rock style but by then the 1990s I had lost any interest in the band.
As for DIAMOND HEAD I remember them getting a fair bit of musical press back around 1981 in SOUNDS (A weekly British music news paper that championed NWOBHM during the 1979-1981 era) and being written about in glowing terms as being "the next big thing" and also being "the next LED ZEPPELIN" before they sunk almost into oblivion until Lars Ulrich of METALLICA started name checking them!.
E-Z