Canadian Alliance MP Rahim Jaffer has been demoted by the party after his executive assistant impersonated him on a national radio show.

Matthew Johnston appeared on a nationally-syndicated phone-in show on Saturday and impersonated the Edmonton-Strathcona MP.

Peter Warren, the show's host, says the hoax was eventually revealed, but not before both Johnston and Jaffer tried to cover it up. Warren says his producer asked Jaffer directly if they had talked to him on the air.

"She reached him at his cafe in Edmonton and said to him, 'Was that you on the interview with Peter Warren on the Corus Radio Network an hour ago?' and his answer was, 'Yes it was. I was happy to do the interview'."

Warren says they finally got an admission from Johnston and Jaffer when they asked them to put their version in writing.

John Reynolds, the Alliance whip, says Jaffer has been suspended from his duties as chair of the party's small-business advisory committee.

"I talked to my leaders and house leaders, and I'm the one that's responsible for discipline as the whip, and I suggested we suspend Mr. Jaffer and we have done that," he says.

Reynolds says the disciplinary measure means Jaffer has been relegated to the back benches. He says Johnston apologized and has since resigned from his position.