Despite their Premiership lead, Manchester United boss Sir Alex Ferguson is adamant this season's Premier League is the toughest he's encountered.

United have not conceded in 13 league games, allowing them to win games by just scoring a single goal.

Nine of their 17 league victories this season have been 1-0, an indication that the division is now tougher.

He said: "There were signs last season that the league was firming up. Games have become more difficult than they have in the past.

"It's very unforgiving. Make a mistake at this level and it's odds-on you will be punished."