The Big Question: Is Glastonbury too big, and is it still Europe's most important music festival?

Just how big is Glastonbury?

Glastonbury 2007, which begins on Friday, is expected to have an attendance of 177,500, making it the biggest since the festival started in 1970. Organisers sold 137,500 tickets in one hour and 45 minutes on 1 April. The first festival, the brain child of Michael Eavis, cost £1, offset by the offer of a drink of milk, and drew a crowd of 1,500. Security this year will be a lot more water-tight than most of the tents, with many festival-goers required to bring proof of their identity and tickets with the name of the purchaser.

For some traditionalists, the event is growing too far from its roots. "This year will be a real test," says the publicist Mark Borkowski. "There are other interesting festivals coming up that are small and beautifully formed." He claims the phenomenal growth of the Edinburgh arts festival has over-commercialised that event and that Michael Eavis faces a similar threat. "Glastonbury is on the edge," he says.

What's the attraction of camping in the mud anyway?

Glastonbury has become the must-have ticket of the British social season, irrespective of whether you actually like music. Though country hotels and Winnebagos are an option for a few, most choose to experience the festival under canvas, meaning they might well finish the weekend soaked through and caked in West Country soil.

For some, the images of sodden festivals of the past are integral to the Glastonbury tradition. The "Year of the Mud," in 1997, made national news bulletins with pictures of festival-goers bodysurfing through brown sludge, but it didn't stop Glastonbury's attendance rising from 90,000 to 140,000 over the course of the following five years.

Heavy rain is again forecast for this weekend, yet many devotees head for Somerset regardless, believing that the magic of the location will outshine the misery of the bad weather. "It's such a great site for a festival, you actually feel as though you've escaped and got out of town," says Steve Phillips, of the music PR company Coalition. Besides, he points out, once you're on site, it's not easy to escape. "There's a Dunkirk spirit because there's nowhere else to go," he adds.

What about all the other festivals?

The success of Glastonbury has spawned a host of other outdoor music events that run from spring to autumn, with many new arrivals appearing last year when Mr Eavis decided to take a year out. The Isle of Wight, Reading/Leeds and V festivals are landmarks on the live rock calendar, with other, more arty, events such as Latitude and Wychwood in Gloucestershire, which incorporate comedy, poetry and other performance arts. British festival-goers have become increasingly willing to head further afield, to events such as Benicassim in Spain and Exit in Serbia.

Yet none of these has the heritage or the scale of Glastonbury. "It's the godfather of music festivals," according to Will Turner, the group CEO of The Hospital, a private members club in London for people in the creative industries. He says the festival acts as a catalyst for future creativity. "When you get people from the creative industries together, things tend to happen."

Paul Stokes, the group news editor of NME, which targets the youthful end of the music buying public, describes a trip to Glastonbury for younger fans as "like a badge that puts you one up on contemporaries who didn't go". Mr Stokes says that the festival is regarded as having become "more adult" than the Reading/Leeds Carling Weekend Festivals. "Glastonbury is still important, it's just that your mum and dad might come along too."

Do bands still care about playing Glastonbury?

The fact that they are almost all prepared to slash their usual fees for the privilege of appearing says it all. Mark Ellen, editor of The Word magazine, says that no other music event has the same stature. "All festivals supply a bigger-than-average crowd for any act, but Glastonbury - like no other - adds a powerful sense of context that makes anyone on stage seem to conform to the spirit of the venture," he says.

Who are the big attractions this year?

Headliners on the Pyramid Stage this year are The Arctic Monkeys, The Killers and The Who. On the Other Stage, the prestige slots fall to Bjork, Iggy and the Stooges and The Chemical Brothers. The Who's publicist, Alan Edwards, says there is no more important place for a rock band to play. "I remember going there with David Bowie and from the stage you could just see this sea of faces going into the distance and over the hills. Backstage, Charles Kennedy, the politician, turned up in his Wellington boots, holding a clutch of vinyl albums and a pen and hoping for Bowie's autograph," he says.

Hasn't it become too corporate?

The marketer Mike Mathieson, of the Cake media relations company, who will be accompanying his client, Orange, to this year's event, says Glastonbury has an altogether different relationship with its sponsors than other entertainment events. "Michael Eavis tells you that you can become involved, but that you have to enhance the festival and do something special," he says.

Mr Mathieson contrasted Glastonbury with the O2 Wireless Festival in Hyde Park. "I couldn't believe how corporate the O2 festival was," he says. But Mr Borkowski says Glastonbury has managed to maintain its ethos. "It's not a money making thing - it's the last of the spirit fests and the others all lack that," he argues.

Does any of this make the world a better place?

Well, Glastonbury is not just about music or, even just about live performance as a whole. The ethos that spreads through the event, and which has been carried forward from its very earliest days, can help to kick start a global environmental campaign.

Stuart Fowkes, of Oxfam, says that Glastonbury is the music festival which the charity values above all others. "It's the Eavis's collective passion for doing things the right way. It creates the right conditions and atmosphere in which people can unite around a cause," he says.

Money raised from the festival has been channelled into Oxfam projects fighting poverty in Kenya and improving sanitation in the developing world through Water Aid. Mr Fowkes adds: "Thanks to Glastonbury, Make Poverty History was huge before the concert even took place. We are hoping the same will happen this year with ICount, the climate change campaign, and that 100,000 people at the festival will sign the petition."

Is Glastonbury about to lose its place as the godfather of festivals?

Yes...

* The event is growing too big and too commercial, and will inevitably lose touch with the unique spirit that has been its heritage

* It will lose relevance to younger music fans who will turn their attentions to smaller, more intimate festivals

* The joys of sleeping in the open air in a wet and muddy field will start to wear thin for the increasingly moneyed crowd

No...

* The history of Glastonbury is unrivalled and brings with it a guarantee of a musical line-up that cannot be matched elsewhere

* There really is something special about the site - the hills help create an ambience that transcends any musical performance

* In his daughter Emily, the festival founder, Michael Eavis, has the perfect successor to ensure that the spirit and its standards continue