Tom Service looks at Progressive Rock, to find out whether it was an apotheosis of rock music, thanks to the influence of classical music, the virtuosity of the performers and the ambition of its structures - or was it a folly of hopelessly over-reaching naivety and vapid pomposity? For a short period in the early 1970s, rock bands such as Yes, Genesis, ELP and King Crimson were boldly experimenting with their music, devising complex pieces that bore little relation to the simple pop song, and exhibiting dazzling instrumental skills. So why did it all go wrong so quickly? Tom consults Dr Sarah Hill, co-editor of the forthcoming Oxford Handbook of Progressive Rock, and also speaks to legendary keyboard wizard (and ex-member of Yes), Rick Wakeman.