Gary Barlow says that after six months of ringing around, he still has a near half-empty bill for the Queen's Diamond Jubilee concert on 4 June.
The Take That singer told BBC Radio 2: "I've been working on this for about six months already to try and get the headline acts booked.
"I'm about sixty per cent through booking the bands. We've already got some pretty big acts: Sir Paul McCartney, Sir Elton John, Sir Tom Jones, JLS, Jessie J, Ed Sheeran, Dame Shirley Bassey, Sir Cliff Richard."
The Queen, Prince Philip and other royals will attend the event, which will be staged at the Queen Victoria memorial at the end of The Mall, in front of Buckingham Palace, which Gary describes as "the best backdrop in the world".
"My focus at the moments is some of the American artists, because we're not only featuring British artists or Commonwealth artists," he said.
"I've got to be honest, it's not a hard sell. Everybody you talk to, you say, 'This is for the Queen' and they're like, 'This is amazing, we want to be involved.'"
He added: "We're going out live on BBC One and it will be beamed around the world. I think there's going to be a couple of billion people to watch this event, all eyes on the capital and all eyes on the artists, and it's going to be a great day for Britain."
A ballot has been launched to give 10,000 members of the public free tickets to the event, To apply go to www.bbc.co.uk/diamondjubilee before 2 March.