From the outside it looks perfectly ordinary. You turn off a broad highway in west London and, leaving the noise of the traffic behind you, stroll down a sedately bourgeois side street. A ceanothus in full bloom is breaking loose from a garden. Opposite runs a long, neatly painted wall. The door that leads through it is discreet. But step in and you find yourself somewhere truly extraordinary. You are standing amid what looks like a mad car-boot sale.

This is the studio of the British pop art pioneer Sir Peter Blake. Or Sir Peter “Sgt Pepper” Blake as he suggests he should be called because his most famous piece of work — the cover for the Beatles’ 1967 album — is what still defines