The Crown Prosecution Service has admitted it has never seen much of the evidence prosecutors are using against Babar Ahmad, who has spent seven years in prison, Green MP Caroline Lucas has revealed.
American authorities are fighting to have Mr Ahmad extradited, a campaign the CPS is supporting because it claims there is not enough evidence to bring a prosecution in the UK. But it has now emerged that it was never given the whole dossier, "save for a few documents".
Mr Ahmad, who was accused of using websites in London - but technically based in the USA - to raise funds for militant groups in Afghanistan and Chechenya in 2003, argues he should stand trial in Britain.
Police arrested him that year but released him without charge. However, he was detained the following year pending extradition and has been in custody ever since.
A petition in support of his cause has attracted more than 140,000 signatures, making it eligible for debate in the House of Commons. Ms Lucas called for that debate to take place and also demanded an enquiry into the failure to pass evidence to the CPS.
It was revealed in a letter to Mr Ahmad's lawyers that the dossier was passed directly from the police to the American authorities.
She told a Westminster Hall debate: "It is my understanding that the CPS knew all along that they didn't have all the evidence, yet they have let Babar Ahmad languish in a maximum security prison with the threat of extradition to the US, under the false belief that the CPS had seen all the evidence against him. This is appalling."
A CPS spokesman said it had never been in possession "of all the US evidence".
Evidence it had been given it said could only legally be used for the extradition process and not a UK trial, it said in a statement.