Also confirmed are Best Fit faves Zulu Winter, 2:54, Veronica Falls and Iceage.
The latest additions in full are as follows:
Sleigh Bells, Veronica Falls, Alt-J, Feeder, The View, The Subways, Bastille, Niki & The Dove, The Futureheads, 2:54, Zulu Winter, Lucy Rose, We Are Augustines, O Brother, Young Guns, Lower Than Atlantis, We Are The In Crowd, Oberhofer, Citizens, SCUM, Crowns, Iceage and Toy.
Already announced are the likes of Foo Fighters, The Cure, Florence & The Machine and The Black Keys.
Reading and Leeds runs between 24-26 August.