The We Will Rock You star's latest project features hits by Metallica, Thin Lizzy, Motorhead, Rainbow, and Rush.

"It's an interesting discussion between a simple riff and a complex riff," May says, explaining the concept behind the three-CD Air Guitar Anthems. "Most of us think simple is great but there are definite exceptions, like Message In A Bottle by The Police - it is the most incredibly complex thing but it sticks in the mind and it's obviously one of the greatest riffs of all time.

"A riff is a riff is a riff... and it's a mystical thing. Either it grabs you or it doesn't and some things can be quite involved or some things can be incredibly simple."

May is currently resting up after cancelling a series of winter concerts. The rocker has been hit by a mystery energy-zapping illness.

He recently released a statement which read: "I have been increasingly battling with a persistent illness which is destroying my energy and my will," adding he had been "strongly advised to rest and heal".