And Ledesma is confident Argentina can give Martin Johnson's men a rude awakening.
"They can say they don't underestimate us but I think that mentally they do. That is a good thing for us," said Ledesma, who plays his club rugby at Clermont Auvergne.
"From the northern hemisphere they are the strongest physically. They have just won the Six Nations, they have just won easily against Ireland in Ireland. They are very confident.
"We have played 18 games in the last four years. The reality dictates they are the favourites but I am not discounting anything by saying so.
"We beat them in Salta (in 2009) and we know we can win."
England manager Martin Johnson has been at pains to stress this week that Argentina boast more threats than just their world-renowned forward pack.
But Ledesma dismissed Johnson's comments as a tactic designed to fire up an England side struggling for motivation.
"We haven't been showing that much (flair) for the last couple of years and historically it's in our culture to play a lot in the forwards," said Ledesma.
"I think he did it to motivate his team. It's difficult to motivate guys when they think they are going to win by 30 points, so I think he did it because of that."
Ledesma and Argentina fly-half Felipe Contepomi are both entering their fourth World Cups, as is England fly-half Jonny Wilkinson.
"It's a great privilege," said Ledesma.
"Fortunately I have my family with me. My parents are here so I am happy and quite proud."
Argentina finished third at the last World Cup, an achievement which ultimately persuaded Australia, South Africa and New Zealand to invite them into a new Four Nations competition.
But the Pumas have since slipped to ninth in the world and Ledesma warned they cannot rest on past glories as they enter a tough group that also includes Scotland, Georgia and Romania.
"We cannot believe that history will repeat itself. That's just an illusion," he said.
"We have to do it tomorrow. It's not about thinking we did it in the past, it's doing it tomorrow and just going for it."
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