In the beginning were the Prog Lords: vast, bloated rock beasts who bestrode the musical world like colossi, force-feeding alienated audiences with their vacuous musical excess. Then came punk to save the world by blowing them all away.

That, at least, is what standard histories of popular music would have us believe. In reality, of course, the progressive rock of the "long 1970s" (c 1967-c 1980) is much maligned and has few champions.

In these days of political correctness and fashion anxiety, prog (along with the Belgians) remains the last safe target of cultural prejudice. When was the last time you saw someone challenged on a bus for loudly mocking the third Wishbone Ash album in the presence of a fiftysomething male or successfully taken to an industrial tribunal for banning Juicy Lucy memorabilia in the workplace?

And yet progressive rock represents a unique moment in British cultural history, the last successful attempt to unite elite and popular culture in a single form, each on its own terms.

É«ºÐÖ±²¥

So, I suggest, we should look at the works of Yes, Genesis, Jethro Tull and the much-derided Emerson, Lake and Palmer (ELP) not as momentary aberrations in the history of British music, but as its finest hour, the latest link in the long and glorious tradition of artistic mould-breaking stretching back to Elgar, Purcell and Byrd, indeed to Chaucer and Shakespeare.

This year is the 41st since the creation of the first concept album, and so it is surely the proper time to reflect upon and celebrate the achievements of popular music's greatest neglected masterpieces.

É«ºÐÖ±²¥

Now, you will probably object, if prog was really so groundbreakingly wonderful, why does it have such an unfortunately naff image these days? The answer, I think, lies in the term "image" itself.

For those who did not live through the glory days of classic prog rock LPs such as Thick as a Brick and Tales from Topographic Oceans, the period lives on largely through TV documentaries and the occasional concert clip in a mainstream music show.

And this is simply not the way to encounter the progressive beasts in their pomp. The early 1970s were a largely pre-video culture, and rock shows were, by today's standards, pretty unsophisticated affairs. Only Pink Floyd's lights and Jethro Tull's stage costumes (on a good night ...) really retain the capacity to surprise or delight. So, look at footage of even the best Genesis concerts of the 1970s, and what you will see is Peter Gabriel in a weird mask, creeping around a stage that wouldn't look out of place in a school hall (but was probably Madison Square Garden), while the rest of the band stand in semi-darkness behind him, trying not to look each other in the eye. How did we brook such low-octane entertainment?

Largely because it wasn't the look of the stage show that mattered. If the lights were good (and they didn't have to be that good to impress in those days), or a roadie came onstage in a rabbit costume to do a dance, so much the better. But, to paraphrase the title of Paul Stump's seminal book on the history of prog, "the music was all that mattered".

Where visual impact was important was in the LP packaging. You cannot underestimate the effect upon the teenage imagination of the 1970s album sleeve as an art form. Long and profitable hours could be spent staring at a Roger Dean illustration across the middle of a gatefold sleeve, imagining the universe of delights on offer within, even before the precious vinyl was removed from the inner sleeve with that familiar crackle of expectant static.

Fans of punk (of which, let the record show, I am one) speak lovingly of the visual impact of a Buzzcocks or Slaughter & the Dogs single, and how, on seeing it for the first time, they resolved immediately to gel their hair into implausible spikes, stick safety pins into their school blazers and strike angry poses in the bathroom mirror.

Well, it was much the same for proggers. When I first saw the cover of Jethro Tull's Heavy Horses, with its image of the flute-playing singer, Ian Anderson, leading a team of shire horses over a verdant meadow, I wanted to run straight out and buy a 100-acre estate in Buckinghamshire. When I saw the sleeve of Curved Air: Live I imagined an alternative career as the band's singer, Sonja Kristina. Such were the dreams of youth ...

But perhaps we rush ahead of ourselves. It may be that there are some benighted readers of Times Higher Education who have not the first idea what I am talking about. What is this prog rock of which I speak? A brief history of the genre might be in order at this stage.

É«ºÐÖ±²¥

"Progressive", for those innocent of its glories, was a label originally applied in the 1960s to any music that sought to extend itself beyond the safe, conservative format of the commercial pop song.

Only later, when contracted to "prog", did it become the brand name of a particular sub-genre of avant-garde rock music, characterised by ambitious lyrical conceits, extended feats of musical virtuosity and lengthy songs, culminating in the now much-derided "concept album" (an entire LP exploring a single narrative or theme). It owed its genesis (as it were) to a unique, and probably unrepeatable, combination of circumstances.

During the mid-1960s, developments in studio technology, including advances in stereo and multi-track recording, increasingly sophisticated and sensitive microphones, phasing and editing coupled with the invention of the mellotron and the Moog synthesiser, encouraged the experimentation of the progressive musicians and allowed them better to realise their ambitions in the studio.

If you could reproduce the sound of a string quartet without hiring one and having to explain what you wanted to a bunch of snooty, classically trained toffs, why not do it? Or why not synthesise a whole orchestra?

And if you could work with orchestral soundscapes, why not experiment with classical forms as well? At the same time the popularisation of stereo record players created a viable commercial market for music that exploited the range of new sounds that these technical advances made possible. Consequently, the late 1960s saw an explosion of rock LPs with obvious classical pretensions: Deep Purple's Concerto for Group and Orchestra, the Nice's Ars Longa Vita Brevis (with its "prelude", four "movements" and a coda, and including an adaptation of Beethoven's Concerto No 9), or ELP's Pictures at an Exhibition are only the most obvious examples.

The Moody Blues famously went into the studio in 1967 with an orchestra to record a rock version of Dvoak's New World Symphony but emerged instead with Days of Future Passed - arguably the first concept album, although Brian Wilson's unreleased Smile and The Who Sell Out also vie for that distinction.

É«ºÐÖ±²¥

"Suites" of linked songs and extended pieces of music, with or without lyrics, also began to feature more frequently. Among the most memorable of these were ELP's Brain Salad Surgery (1973), containing "Karn Evil 9", which younger readers might recognise as the theme tune of ELP fan Jim Davidson's The Generation Game ("Welcome back my friends to the show that never ends ..."), Jethro Tull's Thick as a Brick (1972) and A Passion Play (1973) and Genesis's The Lamb Lies Down on Broadway (1974).

Not content with this, bands also adapted classical or contemporary literary texts as musical forms. Horslips reworked two of Ireland's founding myths as the LPs The Tain (1974) and Book of Invasions: A Celtic Symphony (1976) respectively; Camel wrote an instrumental suite around Paul Gallico's novella The Snow Goose (1975); while King Crimson's song Sailor's Tale alluded to passages in É«ºÐÖ±²¥r's Odyssey, and their album Starless and Bible Black (1974) gestured reverentially toward Dylan Thomas.

Now, one could dismiss this as the worst sort of hubristic nonsense, or "shocking old shite" as a colleague recently suggested, but it surely represents an impressive attempt by popular musicians to transcend the limitations of the pop song and take their art in new directions. It's easy to laugh (oh, go on then ...), but can you imagine today's bestselling pop artists attempting anything even half as ambitious? Until the Kaiser Chiefs produce an album based on the novels of Martin Amis, or Dizzee Rascal gives us his Iliad, I rest my case.

But then the progressive musicians were the product of the unique educational circumstances of the late 1960s. Among the last generations to pass through the classical humanist liberal arts education of the grammar schools, they came of age as the first generation to benefit from the great expansion of higher education in the 1960s.

This was a practical as well as an intellectual advantage. Many of the bands were formed in the common rooms of the new universities and polytechnics. And for those not able to benefit from the seemingly endless grant-funded practice time that the first-year undergraduate syllabuses seemed to offer, the student unions of the new redbrick institutions created a national concert circuit ideally designed for the progressive bands, delivering audiences drawn from the same humanist-educated, aspirational backgrounds as the band members themselves.

So it is no accident that prog represents the last mainstream popular musical movement unashamedly influenced by a broad liberal arts agenda. These groups wrote and sang about the things they had read about in the books and heard in the music they had listened to in school, as this was what they knew best.

They - and their audiences - thought intelligent musicians should be aiming to better the three-minute mantras of commercial pop. The result was music that one felt expanded the mind as well as moving the soul, and went all the way up to 11 when it needed to as well. Contrary to the popular image, the progressives were not classically trained musicians letting their hair down (all right ... some of Curved Air were, and most of Gryphon, and the one in Jethro Tull who recently had a sex change). Nor were they (barring four fifths of Genesis) privileged scions of the upper classes indulging expensive demagogic fantasies.

Their background was similar to that of the punk musicians a decade later: young lower-middle and working-class lads keen to use music as a form of personal expression. Just as punk rebelled against the conventions of musical virtuosity that informed prog, so prog in turn had rebelled against the confines of the three-minute single and what it saw as the blandness and commercialisation of Sixties pop.

Admittedly, by the later 1970s things had gone awry in some quarters. Hubris and commercial success can be a heady blend.

ELP's 1977-78 orchestral tour of the US, when each band member travelled in a separate limousine and had his equipment transported in a personalised, liveried pantechnicon, is the emblematic image of prog having gone one stack-heeled step too far.

But we shouldn't judge an entire decade's experimentation by a few late excesses. The music has endured when much that followed it has faded into obscurity, and many of the seminal acts are once more on the road.

Hence it is a fitting moment to celebrate the achievements of the prog lords of yore. We shall not see their like again. (Unless, that is, we catch Curved Air, reformed and gigging in the UK this autumn, the Keith Emerson Band in Japan, or Jethro Tull, taking a 40th anniversary tour across Europe as we speak ...).

For homework, those readers who have followed the argument so far, can choose one of the following questions.

1. Compare and contrast Walter Raleigh's As You Came from the Holy Land with Jon Anderson's Owner of a Lonely Heart, showing why the latter is better.

2. Choose any piece of music composed before 1910 and demonstrate how it could be improved by the addition of a) a mellotron b) a ten-minute drum solo or c) both.

3. How might the career of either Thomas Tallis or Mozart have benefited from the artwork of Roger Dean?

É«ºÐÖ±²¥

Please refer to work by at least one of the following in your answers: Blodwyn Pig, Van Der Graaf Generator, Barclay James Harvest or Henry Cow.