“This is an album I played on but I can assure you it’s not why I picked it. It’s what I lovingly call a prog-metal album. We’d been mates for donkey’s years and when I was in New York while we were making this Ozzy said he had quite a few Mellotron bits for me to do.

“The first track we did was Perry Mason and Ozzy knew exactly how he wanted it to sound and I told him that it sounded very prog. At that time, for metal bands, the thought of having a keyboard anywhere near them was unheard of. I told Ozzy I couldn’t believe he was making a concept album and he laughed and said, ‘Well we can now!’

“Ozzy is very bright and switched on. He was there when everyone was putting their parts down and would ask people to play things a certain way or change things slightly to get the sound he wanted. He’d had 8-track heads built to fit on a 24-track tape-machine to record the drums with because he wanted that fat sound. I was very, very impressed with how hands-on Ozzy was - he’s a damn sight cleverer than anyone would ever give him credit for.”