Manager Martin Johnson says England must improve their fitness levels if they are to compete with the world's best sides.
Johnson's side beat Scotland 26-12 in their final Six Nations game to match last-year's second-place finish.
"Our guys are fit, but there's fit to play in the Premiership and Europe and there's the fitness to try and beat the best teams in the world," said Johnson.
"The southern hemisphere sides are fitter and can play at a high tempo."
England were beaten 28-14 by Australia, 42-6 by South Africa and 32-6 by New Zealand at Twickenham in the autumn.
But three home victories over Italy, France and Scotland in the Six Nations saw them finish above France and Wales on points difference.
"Some guys [in the England team] are there [in terms of fitness], some guys aren't because they don't know what it takes, they've only come into international rugby this year," Johnson said. "But now they know what it does take.
I always said that there was something there in this squad and it's really starting to come together now
"You saw two very tired teams at the end [between England and Scotland] and whoever can be thinking and acting on their feet in the last 15 minutes is going to win those games.
"We cannot claim to be as good as the southern hemisphere sides at the moment, we can only do that when we start winning games against them."
Despite his admission that northern hemisphere sides still have a lot of work to do to match their southern rivals, Johnson said that his first Six Nations in charge of England had been a "very, very good tournament quality-wise".
"[British and Irish Lions head coach] Ian McGeechan has got real good players to pick a series-winning squad from," said Johnson, who toured with the Lions on three occasions in 1993, 1997 and 2001.
"In some areas he's got some really tough choices, in some areas it's a little bit thinner, but he'll get a top squad out there.
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