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As a music genre, Prog Rock still finds it difficult to be taken seriously. For many, its worst excesses - "concertos" based around sub-Tolkien English pastoral themes, attempting to tour the US with a 30 piece orchestra - have overshadowed many of its achievements.

Alex Mackintosh's Time Shift traces the history of Prog Rock as a genre back to the heydays of 1960s psychedelia, seeing how, for many British musicians and fans who had educated themselves on the R&B circuit, musical extemporisation and concept albums were an exciting departure. Many of the era's best bands - Pink Floyd, The Nice (who later formed part of ELP), King Crimson and Yes - built their success around this experimentation, providing a genuine alternative for a generation who had grown up with Sergeant Pepper and were tired of Top of the Pops.

As the programme reflects, this experimentation often ended in a musical cul de sac or grew in scale to become overbearingly pompous is hardly just the fault of the musicians. In fact, what seem like the movement's worst excesses - Pink Floyd's flying pigs, Rick Wakemen's King Henry VIII on Ice, Peter Gabriel's Genesis stage costumes - were actually conceived with more than a little tongue in cheek. As Steve Hackett maintains, Prog was always closer to panto than pub rock. And, for all of punk's blast of much needed fresh air, it's difficult not to have a little sentimentality for a time when musical imagination rather than product sales was a measure of achievement.