Robert Plant refused to keep working with the band after their one-off concert at London's O2, later released as Celebration Day. A number of vocalists were tried out, including Steven Tyler of Aerosmith and Myles Kennedy of Slash and Alter Bridge.

Page tells Metal XS: "In the run-up to the concert, the only music we played was Led Zeppelin. But we played really, really well. Jason, myself and John Paul Jones played really well together so it made sense to see what we could do, using that same energy with new material."

He continues: "But of course, that's not good enough for other people - they want to keep trying singers out. From my point of view, the most important thing is to concentrate on your strengths, not your weaknesses. With the weaknesses, none of us sang. But we could play."