Simon Cowell has lashed out at Lou Reedfor refusing to allow Susan Boyleto perform his hit Perfect Day on America's Got Talent.

SuBo had been booked to perform the classic track on the US talent show this week. But at the 11th hour, Lou Reed’s management refused to let her sing the song.

According to reports, the I Dreamed A Dream singer burst into tears when she heard the news, refused to perform a different track and flew straight back to Scotland.

Simon vented his anger in an interview on Radio 2, branding Reed's behaviour “petty” and “pathetic”.

“She was supposed to be on America's Got Talent this week. We've flown her over and she is going to perform Perfect Day by Lou Reed,” Simon explained. “Two hours before she is going to perform it we get a phone call. Lou Reed will not allow her to sing Perfect Day.

"This is so petty, so pathetic," Cowell continued. "Loads of people have covered this song. This is a fantastic version. He's now saying, ‘If I'd have known, I'd have given permission’. Well Lou, if you're listening: Do we have permission to put the song on next week? Personal request from me."

In the same interview, the uber-judge admitted that the amazing response Susan received when she first appeared on Britain’s Got Talent caught him off guard.

"It wasn't a great day. She came on and I thought, ‘I don't think this is going to be great, I've just got a feeling here,’ and she started to sing,” Simon recalled.

"I didn't think at the time, to be honest with you, that this was incredible. I remember thinking this is great but Piers and Amanda got it more than I did. Then when I watched the clip back and I saw the whole story; that is when I thought this is going to be huge and I'm going to look like a complete idiot."