"When I was first ill, Brian May came to visit me at my house in Lapworth," Iommi said. "I played him some of my stuff, rock riffs that I'd never quite got round to developing, or decided not to use. He said I ought to do something with them.

"It's early days yet, and all my attention in on Sabbath for the foreseeable future, but we may well find some way of working together on them, and making them available in some shape or form.

"One of the ideas we had is that we could make the riffs available, get fans to use them in songs of their own, and see what they come up with. That way they'd effectively be recording with Brian and myself."

May adds: "I heard some of the hours of unreleased guitar jams Tony has on tapes and hard drives," he said. "I thought it would be great to make a compilation out of them.