Mr Clegg said there was 'no excuse' for government not to intervene
Nick Clegg has called on the prime minister and home secretary to "do the right thing" and block the extradition of computer hacker Gary McKinnon.
The Lib Dem leader accused ministers of "hiding behind weasel-worded legal excuses" and demanded that Gordon Brown and Alan Johnson intervene in the case.
Mr McKinnon, 43, has been denied leave to appeal to the new UK Supreme Court against his extradition to the US.
The Home Office has refused to comment while the legal case continues.
Mr McKinnon has admitted hacking into 97 US government computers, including those of Nasa and the Pentagon.
He insists he was looking for evidence of UFOs but US authorities want to try him under anti-terrorism laws, which carry a maximum penalty of 60 years in prison.
Both the Lib Dems and the Conservatives have criticised the UK's extradition treaty with the US. They say it is unfair to British citizens because of the lack of reciprocity shown by the American authorities.
Following the failure of Mr McKinnon's appeal on Friday, Mr Clegg told the BBC his case demonstrated "precisely why we, the Lib Dems, were so staunchly opposed to this treaty right from the beginning".
"This is wrong. It must be stopped, and Gordon Brown and Alan Johnson can stop it by trying Gary McKinnon here under British law rather than shipping him off to a jail in America," he said.
"The Home Office and the government are hiding behind weasel-worded legal excuses.
"There is no excuse not to do the right thing and the only right thing to do is to prevent this vulnerable man being sent over to America."
Mr McKinnon has Asperger's Syndrome and his lawyers say extradition could have "disastrous consequences" for his health.
The former shadow home secretary David Davis said: "The reason this decision has been arrived at is because the British government created a set of laws and agreements which, masquerading as anti-terror laws, actually disadvantaged a whole range of British citizens.
"It is long past time that this travesty of justice was put right."
A Conservative-led debate in the House of Commons in July failed to force a review of the laws.
During the debate the home secretary said the act had simplified extradition rules while still protecting suspects' rights.
At the time Mr Johnson denied claims the law was one-sided, saying the burden of evidence required to secure someone's extradition on either side was "essentially" the same.