Asked about the US-UK extradition treaty which has been described as "one-sided", Attorney General Dominic Grieve QC said there were "underlying fundamental problems that are not very easy to address".
"I think there's a lack of public confidence in the US justice system," he said.
There were perceptions in Britain that the US justice and penal systems were "harsh and disproportionate", leaving Britons "uneasy and uncertain", he added.
He told the MPs these concerns were "not readily curable".
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Deputy Prime Minister Nick Clegg launched his election battlebus today with an attack on the Conservative Party.
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David Cameron will stand down as Conservative leader ahead of the general election expected in 2020, Iain Duncan Smith said.