Manchester United boss Sir Alex Ferguson has claimed that there would be a House of Commons inquiry if his side got the same number of penalties as rivals Manchester City.

City have been awarded four spot kicks in their last three home games and Ferguson is wary of them getting another when the two sides meet on Sunday.

Ferguson also admitted that City are now United's biggest threat but is confident that they can see off their challenge as they have done with Liverpool, Arsenal and Chelsea in the past.

"The number of penalty kicks they get - 21 in the last year or something like that. If we got that number of penalty kicks there'd be an inquiry in the House of Commons. There'd be a protest," said the veteran manager.

"Liverpool and United games over the last 25 years have been unbelievable. They've always been the most important games. It's shifted because at this moment Liverpool aren't challenging for the league like City are.

"City are our biggest threat and we're their biggest threat, so that's changed. Their fortunes changed the minute Sheikh Mansour took over. We know the minute that happened it was going to be a different ball game altogether. But, as we have in the past, we have to accept their challenge like we did when Chelsea came along and when Arsenal overtook Liverpool in the early '90s. We have to do it again."

Despite Ferguson's claims, United and City have both been awarded the same number of penalties, 21, since the start of the 2010-11 season.