Manchester United boss Sir Alex Ferguson has criticised the transfer policy of rivals Manchester City, after labelling Richard Dunne "the buy of the season" following his move from Eastlands to Aston Villa last summer.

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GettyImagesAston Villa's Richard Dunne has impressed since his £5 million move from Manchester City last summer

Dunne has excelled since his £5 million arrival at Villa Park, during which time City's new expensive defensive signings Kolo Toure and Joleon lescott have struggled to gel.

And Ferguson believes that Dunne, who is certain to start against United in Sunday's Carling Cup final, has been key to an improved Villa defence this season.

"Dunne is the buy of the season," Ferguson tols the Mail. "£5million for him was outstanding business. He and James Collins have helped Villa improve defensively this season.

"They are a professional, organised team and Martin O'Neill has done a terrific job with his players.Martin has done a good job in a quiet way without spending a great deal of money."

Villa have the best defence in the Premier League this season having conceded just 21 goals, but Dunne and Collins will have their work cut out against the league's top marksman Wayne Rooney - who has netted 23 goals this campaign.

However, Ireland defender Dunne had revealed his team are in confident mood ahead of the final, which provides Villa an opportunity to win their first major piece of silverware since the 1994 League Cup - a compettion they won after beating United in the final.

"Most people probably expect Manchester United are going to win," Dunne said. "But we are going there full of confidence with a genuine belief we can beat them.

'We have generally done well in the big games this season, having beaten United and Liverpool away, and Chelsea at home. We are in good form and know that on our day we're a match for any side.'