One of the UK's biggest music festivals will now become a three-day event, organisers announced yesterday. T in the Park will run at Balado, near Kinross, in Perthshire, from Friday July 6 to July 8. For the first time, the festival arena will open to around 50,000 campers on Friday night when Arctic Monkeys will headline the main stage. On Saturday, American rockers the Killers will jointly headline with Razorlight. In total 35,000 tickets have been sold, and another 40,000 will go on sale tomorrow. To cut touting, ticket purchases will again be limited to two a person.