Not long after the brochure for this year's Proms went to press, the English countryside found itself making headlines in an unprecedented way. Though the foot-and-mouth outbreak no longer leads the British television news every evening, there are still new cases reported most days.

"I think the crisis has opened an interesting debate, which the music reflects," says Nicholas Kenyon, the Proms' controller of music. "Why do people feel so passionate about the countryside? It seems the death of farming is a much more important issue in people's minds than, say, the closure of a steelworks, because people feel their relationship with the landscape is a key part of Britain's heritage.

"And yet the irony is that farming has changed the landscape out of all recognition in some areas. We wanted to provide a perspective against which people could think about these issues themselves."

One of the big commissions this year tackles the subject head-on. Knotgrass Elegy by Sally Beamish is an oratorio describing the ravaging of Earth by pesticides and herbicides. It features a character called the Tempter, who hands out agrichemicals, destroying knotgrass and the beetles that feed on it.

With dozens of planning applications every week for greenfield housing estates and shopping centres, the English countryside is under enormous threat. Yet Kenyon believes it still provides a fertile source of inspiration for today's composers.

"Even though they are having to be much more international these days, I don't sense any lessening in the connection between music and the countryside," he says. He cites James MacMillan's new Proms work, Birds Of Rhiannon. "He is responding to the landscape, and using its myths and legends."

Amid the flag-waving of the Last Night of the Proms, Leonard Slatkin will conduct The Fall Of The Leaf, a little-known work by Gerald Finzi. He is delighted the composer is finally getting his day. "Years ago I recorded Finzi, and my record company said: 'He's so obscure we can't release it.' They said the public simply wouldn't be interested."

Though an American, the new chief conductor of the BBC Symphony Orchestra is widely praised for his interpretations of English composers. It runs in the family; his cellist father, Felix, was the first to play Finzi in the US. "I think he's the perfect example of someone writing truly descriptive music," says Slatkin, who compares him to Elgar and Vaughan Williams. "Each one of them created a very different interpretation of how they believed the landscape would sound."

Arts festivals thrive on anniversaries, and this year's Proms are no exception. Finzi and Edmund Rubbra were born a century ago, and it's 50 years since the death of Constant Lambert. The three men helped define a new era in British music, using the rural landscape they lived in as a principal source for their work. All were prolific - Rubbra composed 11 symphonies - yet in the past few decades their music has rarely been performed on the concert platform.

Kenyon feels this is their moment. "There was an era when the Proms neglected this kind of repertoire, but we've been gradually moving back towards it. I think it's important, though, only to do the good works, the ones you really believe in. You have to accept that they also composed some quite bad music."

The "good" works include Lambert's symphonic cantata The Rio Grande and Finzi's Shakespearean song cycle Let Us Garlands Bring, placed alongside better-known works such as Britten's English folk song settings and Vaughan Williams's Pastoral Symphony to create a theme running across the season. This year, that includes 73 concerts at the Royal Albert Hall - capacity 5,500 - and eight chamber recitals at the nearby Victoria & Albert Museum.

Andrew Burn, the secretary of a trust set up to promote Finzi's music, suggests performance of four of his works at the Proms heralds the beginning of a revival of interest in the period. "It's music that is still unfashionable. Orchestra managers are as dubious about putting on, say, Bax or Rubbra as they would be about Mark-Anthony Turnage or Judith Weir." But, says Burn, the rapidly growing number of CD releases of this music, on labels such as Chandos and Naxos, illustrates its new popularity. "The music critics who regularly damn these composers seem to be out of step with what the public think. We've been staggered by the amount of interest this year in Finzi alone."

Earlier this year, Kenyon made a journey to the tiny Hampshire village where Finzi lived. "I realised that there is an incredible aura about the place. It is still very unspoilt there, and you really recognise the way the countryside around resonates in his music."

Ironically, few of these country composers were Anglo-Saxon "men of the land". Though the many websites dedicated to them contain pictures of men leaning on wooden gates outside pretty cottages, their backgrounds were often rather more exotic.

Constant Lambert had Russian and Australian parents. Gerald Finzi was of Italian Jewish ancestry. "Finzi really seemed to play down his Jewishness," says Kenyon. "He really tried to turn himself into an English country squire. It was very interesting listening to his cello concerto the other night and noticing that there are clear musical illustrations of his Jewish roots."

Finzi's rural life didn't mean he was any less aware of world affairs - he took in Jewish refugees before and during the second World War. In many ways he was an obvious pacifist but, unlike Britten or Tippett, he saw the need to stand up to the horrors of fascism, turning down an easy job with the BBC music department to work instead for the ministry of war transport.

Proof, were it needed, that the English pastoral composers were realists, and not completely wrapped up in a bucolic world of walks on hills and harvest festivals.

The first week of this year's Proms saw a performance of Ralph Vaughan Williams's Pastoral Symphony. Philip Heseltine, another rural composer, who wrote under the name Peter Warlock, erroneously described the symphony as like "a cow looking over a gate".

Though clearly inspired by the countryside, it is actually an eloquent war elegy, influenced by Vaughan Williams's years in the army as a medical orderly during the first World War. "A requiem to the dead of Flanders" is how Andrew Burn describes it.

Vaughan Williams's friend George Butterworth is best known for his settings of A.E. Housman's 1896 poems A Shropshire Lad, sung last week by the baritone Thomas Allen. One of them, The Lads In Their Hundreds, describes young men travelling to Ludlow Fair. Its lines are chillingly prescient of what was to happen 20 years later. "The lads for the girls and the lads for the liquor are there / And there with the rest are the lads that will never be old".

Butterworth was one of those who never grew old, killed by a sniper's bullet at the Somme. Elizabeth Lutyens, a radical English composer of the period, got it very wrong when she invented the phrase "cowpat music" to describe the work of her rural colleagues.

Ernest Rubbra's work was also touched by war. He dressed in military uniform at the Proms in 1942 to conduct the premiere of his Fourth Symphony, revived this year by the BBC National Orchestra of Wales and conductor Richard Hickox. His composing base was the Chiltern Hills but, again, his output was not necessarily about the countryside.

"Rubbra's music has a real toughness and grittiness," says Burn. "People who don't like it call it grey, but that's wrong; he has a bleak, dark side to his music." Kenyon recalls him being described as "Bruckner on speed" and points out that "he was a very tough symphonic thinker, of a very peculiarly English mould".

Again, Rubbra was far from the stereotypical image of a gentleman composer. Brought up by poor parents, he started off as an errand boy, and then become a railway clerk, his evolution into full-time musician hard fought for.

The "countryside" season may be a one-off, but the English landscape is celebrated at least once a year at the Royal Albert Hall, when thousands of dinner-jacketed Prommers wave their national flags and sing along to Jerusalem, William Blake's celebration of England's "green and pleasant land".

It is the ultimate piece of idealistic writing, reflecting a world so beloved of the pastoral composers - a Utopian England. A world that never existed, and probably never will.

The BBC Proms run at the Royal Albert Hall, London, until September 15th. Full details are available from www.bbc.co.uk/proms. Every concert is broadcast live on BBC Radio 3, with selected concerts on BBC television and Lyric FM