I’d been a prankster from school days, and it carried on into the band. Bill Ward, our drummer, took the brunt of the jokes. If I didn’t play him up he’d say: “Are you okay? You haven’t done anything to me today.” He loved it, though maybe not everything we did to him.

In 1973 we went to record an album in Beverly Hills. We rented John DuPont’s house [heir to the DuPont chemicals fortune]. It was a lovely place — ballroom and everything. We went rummaging around and found this gold spray paint in the garage. I thought: “We’ll get Bill with that.” We waited until he’d had a few drinks and was out of it, took all his clothes off, then sprayed him gold from head to toe. Then we found this tin of lacquer and lacquered him. He was violently ill when he came round.

So we phoned an ambulance. You can imagine what they thought when they arrived — seeing this bloke lying there, naked and sprayed gold. They asked us if we realised what we’d done, and said we could have killed him by blocking up all his pores. They were really pissed off. They gave him a shot of something to sort him out and told us to clean him up. So we went back in the garage and found some paint stripper. His skin went this horrible red, really sore. We laughed about it the next day, but God, it wasn’t funny on the night.

Bill and I used to have this party piece where I’d set him on fire. I’d pour alcohol on him — the studio alcohol we used to clean marks off the machines. I’d pour it on his hands, light it, flames would appear, and it would burn off. The effect was completely superficial — no damage done. One day I wanted to do this trick for our producer. I said to Bill: “Can I set fire to you?” “Not just yet,” he said, “I’m busy.” A couple of hours later he said: “I’m going home now, Tone. Do you want to set fire to me or what?” I got the alcohol, poured it over him, and as I lit him he went whoomph. All his hair, his beard, everything went up in flames. He dived on the floor. I thought he was laughing, but he was screaming — and I was still pouring this stuff over him. He got third-degree burns. His mum phoned me and said: “You barmy bastard! It’s time you grew up. Our Bill might have to have his leg off.” I felt bad.

Because I used to be the only one who could drive, it was up to me to take the band to and from gigs. But driving them home got boring, because everyone would fall asleep. One night I found this road in Birmingham that looked identical to the one Ozzy lived on. I decided to drop him off there. I watched him as he got out of van, half asleep, and tried to get into someone else’s house at 4 in the morning. Then I drove off. Ozzy lived about a mile away. I did the same thing for a few nights before he finally said something. So I left it for a month, then he’d fall for it again.

On a flight once Bill’s language was particularly colourful. The woman sitting in front of him turned round and said: “Wash your mouth out with soap.” So he went into the toilet, chewed this bar of soap, and came back foaming at the mouth. “Is that all right?” he asked her. Another time, driving across the desert in the States, we came across a wooden shack that had “Fireworks” written on the door. Ozzy went in and bought all the fireworks in the shop. That night, after we’d all gone to bed in our hotel — it was newly refurbished — I woke to see smoke coming under my door. I looked through the peephole and saw Ozzy at the end of the corridor, letting off rockets. He caused so much damage. The police came, but he didn’t stop. He was totally out of it, still shooting the rockets. The sprinklers came on and all the guests ran down to the lobby in their pyjamas, thinking there was a fire. The police arrested Ozzy. They told me if we wanted him out, I’d have to go to the station and bail him out. I told them to keep him for the night. I wanted to get some sleep.

I’ve known Ozzy since I was 11, from school, and he hasn’t changed. He still calls me at the most peculiar times — at 3 in the morning when I’m asleep — and leaves silly messages. A lot of people ask me what it’s like seeing him in his TV show, and I tell them that now they can see what I’ve had to put up with for 40 years.

But you’ve got to have fun as a band. If you don’t, you’ll explode. You need some kind of release. A lot of the things that went on were day-to-day occurrences — another day, another joke. This is just a taster of what went on. But this band is like a brotherhood. We have our ups and downs, but we try to make whatever we do enjoyable. We’re lucky, at our age, to still be able to do this. It’s fantastic. Especially since we’ve stopped drinking and can do it all without falling over.

Tony Iommi presents Black Sunday on Planet Rock at 7pm on Sundays. Tune into DAB Digital Radio or visit www.planetrock.com or www.iommi.com