Terror suspect Babar Ahmad is expected to make a last-ditch appeal against his imminent extradition to the US today.
Mr Ahmad and Syed Talha Ahsan, both of Tooting, are accused of running a jihadist website which gave material support to terrorism.
Last week Mr Ahmad's sister, Dr Amna Ahmad, told the Wandsworth Guardian of her hope a private prosecution request could save her brother from extradition.
But the Director of Public Prosecution (DPP) rejected the application to privately prosecute them both yesterday, which had been requested by businessman Karl Watkin.
He told the BBC he instructed his lawyers to prosecute because the crimes took place in the UK and the CPS has not acted
Mr Ahmad's last hope now is for an injunction to halt his deportation which he is requesting at the Royal Courts of Justice, alongside Abu Hamza, Khaled al-Fawwaz and Adel Abdul Bary. Mr Ahsan, is not mentioned on the court list.
Yesterday MP Sadiq Khan said he was disappointed the DPP rejected the private prosecution.
He said: "I am very disappointed by the decision of the DPP. The families of my two constituents are understandably devastated by this news.
"It is still unclear why, if the evidence the American authorities rely upon came from Britain, and at all times the offences were supposed to have been committed occurred when both men were in London, they cannot be charged and tried in the UK"
Mr Khan also called on the media to stop grouping Mr Ahmad and Mr Ahsan with Abu Hamza, who has been convicted of hate and terrorism-related crimes.
He said: "It is important to remember that Babar Ahmad and Syed Talha Ahsan are very willing to stand trial in the UK.
"The American authorities are accusing them of committing serious crimes whilst in the UK, backed up with evidence collected by the Metropolitan Police.
"They are not trying to avoid standing trial, rather they feel that they should be tried in the country where they are accused of committing the crimes - which is also the place where their family and legal representatives are."