Glastonbury Festival does not officially begin until tomorrow, but thousands of fans have started arriving on site today (June 23) to set up camp for the week ahead.

The gates are open at Worthy Farm in Somerset and those who do arrive early will be able to watch the World Cup on a giant screen. Further England games will be screened if the team qualifies for the next round today.

The festival is a sell-out - 140,000 tickets were available, while the total capacity is 177,000 including staff, merchants, performers and crew. And there is even a forecast for hot weather over the weekend, in contrast to the rain, mud and flooding of previous years.

But in the 40th anniversary of the festival, there was a setback when Bono's back injury forced U2 to pull out of their Friday night headline slot.

Gorillaz quickly stepped in to replace U2, which made sense given the success of their third album "Plastic Beach" and the potential for guest stars. Snoop Dogg, who plays further down the bill on Friday, seems likely to join Gorillaz on stage.

Muse and Stevie Wonder are the other headliners, while other performers over the weekend on the Pyramid Stage include Dizzee Rascal, Vampire Weekend, Willie Nelson, Scissor Sisters, Shakira, Jack Johnson, Slash and Norah Jones.

The Other Stage has secured the Flaming Lips, Hot Chip, Florence and the Machine, Editors, the National, MGMT, Orbital, LCD Soundsystem and the Pet Shop Boys, who headline on Saturday night (June 26).

The BBC will have rolling coverage on its TV and radio networks, and packages of performances will be sold to international broadcasters and broadcast in the month after the festival (Billboard, May 15).

Dairy farmer Michael Eavis has run the festival since 1970, when Marc Bolan performed. The event has rested for some of the years since then. Eavis's daughter Emily has been helping him to run it for the last decade.

The festival is a success but has avoided becoming too commercial. Sponsors such as mobile phone companies are only allowed if they bring a tangible benefit: Orange, for instance, will erect a phone mast. Eavis has also resisted any brand extension, declining to license CDs or launch new editions of the festival in other countries.

The Financial Times reported that Glastonbury's profits for the 2008 financial year were just £18,000 ($26,800) on a turnover of £24 million ($35.8 million). Michael Eavis clearly invests in the festival - including environmental measures and an extensive line-up - as well as giving £1.5 million ($2.2 million) to charities in 2008.

The FT said Eavis receives a salary of £60,000 ($89,400) and his farm is paid £500,000 ($744,800) for loss of earnings during the festival.

Eavis avoids the impact of high rents because he owns the land. Since 2002, Glastonbury has had a relationship with Live Nation and its U.K. company Festival Republic. Its managing director Melvin Benn has a key role in organizing Glastonbury.

Emily Eavis said that they also direct Glastonbury artists to Live Nation events where they earn higher fees. Glastonbury pays artists no more than £300,000 ($446,900) she said, and so artists such as Bruce Springsteen were directed to more commercial events such as Live Nation's Hyde Park Calling on the same weekend. He performed at both events last year.

Major artists want to play the iconic festival - it also gives them major exposure on the BBC TV and radio channels - so accept the smaller fees available for Glastonbury, especially if they can supplement that with other U.K. festival shows.