I was there too - born in '57 and did most of my formative listening in the very late 60s, early 70s. I guess your gang of mates called stuff different to my gang of mates. We described Zep and Deep Purple as being heavy rock. Black Sabbath were the first 'heavy metal' band, I believe the expression was coined because of their industrial roots, and the name stuck for the genre of music kind of followed on from that - more to do with distorted, not just overdriven, guitars. But my crowd never referred to Led Zep or Deep Purple as heavy metal, ever. The more complex music from bands like Yes and Genesis were called prog rock. NWOBHM came long a tad later. But maybe different location had a different perspective.