Will Carling has warned England that they must be prepared for the hostility of the Millennium Stadium when they face Wales in the Six Nations on Saturday.
England will head to Cardiff looking to clinch their first grand slam since 2003 and Carling, who captained England to three grand slams during the 1990s, believes that Stuart Lancaster's men must be mentally equipped to face a passionate Welsh crowd.
"For England to win a Grand Slam in Cardiff is about as hard a task as you could get, probably not quite as hard as winning a World Cup in Australia but it's pretty close in terms of its rivalry," Carling told Sky Sports News. "It will be right up there. If they manage to do it, it will be an incredible achievement.
"Around 80% of England's week will be mental. Most of it will be about getting their minds ready for what they will face in terms of atmosphere at the Millennium Stadium.
"They must also understand the emotion of the occasion, what the crowd will be like and how passionate the players will be."
England beat Italy 18-11 in their last Six Nations outing on Sunday.
