Strictly Come Dancing judge Craig Revel Horwood has criticised talent show contestants Susan Boyle and Wagner as "one hit wonders".
The Australian-born dancer said some of the stars produced by shows like The X Factor took "jobs away from people who have been training for years".
He told Phil Williams on Radio 5 live Breakfast: "I don't have respect for the Wagners of this world and the Susan Boyles of this world as they're one hit wonders.
"I'm talking about the value and quality of the voice."
He added that Boyle, whose second album has been nominated for a Grammy award, "basically lacks technique".
He said: "There are people like opera singers who train for years and years and years to perfect their voice, maturing it, and I'm afraid that Susan Boyle doesn't fit that category for me.
"What proved it was that every one of the judges stood up for her when she sang Memory when she was totally out of tune, and they didn't say anything - they lied to her - and number two, she was completely out of tune.
"When she got to the key change moment there was no build, there was no excitement, there was no drama, she didn't understand the story - that's what I'm talking about. You get Elaine Paige singing that song and you'll get something extraordinary."