The top prosecutor in England and Wales has refused to consent to the private prosecution of terror suspects Babar Ahmad and Syed Ahsan.
Keir Starmer QC, the Director of Public Prosecutions, said the documents provided by British businessman Karl Watkin were "very short, lack any meaningful detail and do not provide any real support for a prosecution".
Mr Watkin, a campaigner against the UK's extradition arrangements with the United States, made the attempt to bring legal proceedings against the pair in the UK to avoid "outsourcing the country's criminal justice system" to the US.
Mr Starmer went on: "The underlying evidence in support of these alleged offences is in the possession of the USA.
"In the circumstances, I have refused to give my consent to Mr Watkin to bring a private prosecution against Mr Ahmad and Mr Ahsan for offences under the Terrorism Act 2000."
Mr Ahmad has been in jail without trial since 2004 while fighting extradition and has pleaded to be charged and tried in Britain.
The pair are accused of being involved in a website which encouraged terrorism and which, while operated from London, was hosted in the US.
Neither has been charged with an offence in the UK relating to the website Azzam.com, even though the investigation by US authorities includes evidence seized by the Metropolitan Police. The CPS has refused to prosecute the men.
Mr Starmer's decision was announced as Ahmad launched a High Court bid to halt his removal from the UK.
The computer expert's judicial review application is now expected to be heard tomorrow along with that of radical cleric Abu Hamza and another suspect, Khaled Al-Fawwaz.
The men are seeking injunctions preventing extradition to the US.
Rejecting Mr Watkin's bid for a private prosecution, Mr Starmer said the attempt relied on "two statements and a number of documents".
"The two statements purport to have been signed by Mr Ahmad and Mr Ahsan themselves but they are very short, lack any meaningful detail and do not provide any real support for a prosecution," he said.
Most of the documents provided appear to have been printed off from websites.
"As they stand, they are probably inadmissible in evidence but, in any event, they do not provide the necessary links between Mr Ahmad and Mr Ahsan and the charges that Mr Watkin proposes to bring under the Terrorism Act 2000.
"Any prosecution on such material alone would be bound to fail."
Mr Starmer added that the Metropolitan Police only submitted "a small number of documents" relating to Mr Ahmad in 2004 and does not intend to refer any further material to the Crown Prosecution Service (CPS) for consideration.
And any suggestion that material provided by the United States could be used in support of a prosecution in England and Wales is "misconceived", he said.
"That material was provided in accordance with the requirements of the Extradition Act 2003 solely for use in the extradition proceedings, which relate to the wider charges alleged in that jurisdiction."