Terror suspects Babar Ahmad and Syed Ahsan are to challenge a decision of the top prosecutor in England and Wales not to consent to them facing private prosecutions in the UK
Both are fighting extradition to the US where they are wanted on terrorism charges.
Keir Starmer, the Director of Public Prosecutions, said yesterday the documents provided by the would-be UK prosecutor - British businessman Karl Watkin - were "very short, lack any meaningful detail and do not provide any real support for a prosecution".
Today Phillippa Kaufmann QC, appearing for both men, announced at the High Court in London that they intended to seek a judicial review on the grounds that the DPP had reached "an unlawful decision".
Ms Kaufmann made the announcement as Ahmad and Ahsan joined other terror suspects, including radical cleric Abu Hamza, in a separate legal challenge to the Home Secretary's decision to sanction their extradition.
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.
Refusing consent for the proceedings, Mr Starmer said: "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.