PRE-SALE tickets for the 2011 Sonisphere Festival at Knebworth are now available.

The third Sonisphere will take place in the grounds of the Hertfordshire stately home from July 8 to July 10 with American metallers Slipknot and Scottish rockers Biffy Clyro the only confirmed headliners so far.

The third big name act will be announced soon.

O2 customers and members of Sonisphere FMC and social communities were able to buy weekend camping passes to the rock and metal event from earlier today (Wednesday).

General tickets – with a three-day festival camping ticket costing �165 – go on sale at 9am from Friday.

Organisers have also introduced a special ‘Sonisphere tourist offer’, a spectacular upgrade on last year’s buy-one-get-one-free deal.

For 2011, early-bird ticket buyers have the choice of not one, but three extra festivals abroad.

Sonisphere Knebworth goers will be able to apply for either a free ticket for Sonisphere in Poland, plus a free ticket for Sonisphere Czech Republic, or a free ticket for Austria’s Nova Rock Festival on June 11-13, where System of a Down will be playing alongside Sick of it All and Volbeat.

Free tickets are subject to availability and will be issued on a first-come first-served basis.

Sonisphere is also repeating its hugely successful deposit scheme, allowing festival-goers to secure their ticket now – and their free bonus ticket if ordered before the new year – without having to immediately pay the full price.

Ordering tickets before January 4, 2011 will also beat the VAT increase.

For more ticket information go to Sonisphere’s official website.