A Briton fighting extradition to the United States over terror charges risks having his human rights breached, a court has been told.
Babar Ahmad, pictured in green, faces US military custody
Babar Ahmad's lawyers fear he could be transferred to military jurisdiction if he is sent to the US.
Under military jurisdiction, he could be given the death penalty.
The 31-year-old computer expert from London is accused of running websites to raise money for terrorism in Chechnya and Afghanistan.
Lawyers for the US government want a short adjournment while they investigate whether a transfer to military jurisdiction once Mr Ahmad was in the US would be a possibility.
Edward Fitzgerald QC, appearing for Mr Ahmad, said: "This is a case of the utmost importance and the issues for the defendant couldn't be more grave."
He said there had been no promise from the US Government that Mr Ahmad would not be transferred to military jurisdiction. He said it had been "deafening in its silence".
They had not done so because being moved to military jurisdiction was "something that could happen".
He added: "And if there is a real risk of transfer to military custody there is also a grave and serious case that such a transfer would involve a flagrant denial of justice."
The US government's legal team have requested a short adjournment, which District Judge Timothy Workman said he was "minded" to grant.
John Hardy, for the US Government, added: "We accept submissions made if he were transferred to military jurisdiction there is no apparent bar to the imposition of the death penalty or transfer to a third state. So the question is, is it a real risk of transfer to military jurisdiction?"
In claims dating back to 1997, the US government accuses Mr Ahmad of "conspiring to support terrorism", saying he "sought, invited and solicited contributions" via websites and emails.
The US also claims Mr Ahmad had plans for one of its Navy battle groups in the Gulf, including comments on how ships were vulnerable to attack.
If Mr Ahmad loses the hearing at Bow St Magistrates' Court in London, which is expected to last two or three days, it will be up to the home secretary to decide if he should be sent to the US.