Until earlier this year, a squat sculpture nestled rather unobtrusively outside 20 Manchester Square in Marylebone, an address once made famous by the cover of a number of albums by the Beatles. The building has since been renovated into smart, slightly anonymous offices and the sculpture suited it. Few knew that it was a work by Tony Cragg, who towards the end of the 1980s was one of Britain’s best known artists, winning the Turner Prize in 1988 and representing the country at the Venice Biennale the same year.