Franz Ferdinand are among the headliners at the split-site festival

All tickets have sold out for the three-day event, with more than 80,000 rock fans at each site.

Fans who purchased special "early bird" tickets were able to enter the sites from Wednesday, braving the weather to bag a prime camping spot.

Other bands appearing during the weekend include Kaiser Chiefs, The Streets and Placebo.

Arctic Monkeys play the main stage this year, after packing out a smaller side-stage in 2005.

Hundreds of fans had to stand outside the tent to hear the Sheffield band, who had released only one single at the time.

New safety barrier

Festival organisers have installed a second security barrier in front of the festivals' main stages in an effort to stop fans being crushed when such popular acts take the stage.

MAIN STAGE HEADLINERS Friday at Reading Saturday at Leeds Franz Ferdinand Kaiser Chiefs Yeah Yeah Yeahs (above) Saturday at Reading Sunday at Leeds Muse Arctic Monkeys The Streets Sunday at Reading Friday at Leeds Pearl Jam Placebo My Chemical Romance

"The idea is to create a front section for as many people as possible but reduce the additional pressure from the thousands behind," said Melvin Benn, managing director of festival organiser Mean Fiddler.

"It is a secondary barrier but not a golden circle," he added. "You will not need a special pass to get in."

Elsewhere around the festivals, which run from Friday to Sunday, Primal Scream and The Raconteurs - featuring Jack White from the White Stripes - headline the NME/Radio 1 stage.

Mercury nominees Hot Chip appear alongside easy listening cover band Nouvelle Vague and hotly-tipped rockers The Fratellis on the Carling stage.

Eclectic bill

Belgian dance act Soulwax are taking over the dance tent, putting together an eclectic bill of live acts and musicians, with support from Coldcut and Mobo-winner Sway.

Russell Brand, star of Big Brother's Big Mouth on E4, has had to cancel his headlining appearance in the comedy tent after a bout of laryngitis.

Mark Steel takes his place, with Stewart Lee and Simon Amstell - recently named the new host of BBC Two quiz show Never Mind The Buzzcocks - also appearing.