Ten terror suspects facing deportation from the UK helped create the "climate and opportunity" for the 7 July London bombings, a court has heard.
Abu Qatada arrived in Britain seeking political asylum in 1993
The 10 were all "dangerous men", Home Office barrister Sean Wilken told a bail application hearing by the Special Immigration Appeals Commission (Siac).
But Ben Emmerson QC, representing seven of the men, told the London panel they had "no connection" with the attacks.
The men, who include radical cleric Abu Qatada, were held in raids last month.
Britain is trying to negotiate with a number of countries to ensure the detainees would not face torture or the death penalty on their return.
The 10 were taken into custody on 11 August as part of a crackdown on terrorists and their supporters in the wake of the 7 July suicide bombings in London.
Abu Qatada is the only one to have been named. The others are known only as A, B, G, H, K, P and the Algerian nationals Q, I and T.
All of the applicants are dangerous men. They all pose threats to the national security of the UK and its citizens
Home Office barrister
At least nine of them had previously been detained before being released and made subject to control orders and curfews in March.
Mr Wilken, representing the Home Office, said the 10 had helped create "the climate, the motivation and the opportunity" for the 7 July attacks.
He told the hearing: "All of the applicants are dangerous men. They all pose threats to the national security of the UK and its citizens."
He said none had any right to be in Britain and all had the motivation to abscond.
"We say that when they have absconded they would resume their activity and would be a threat to the UK and its citizens," he added.
Abu Qatada and the men known as A, B and K all had a history of absconding and A, B, G, H, K and P had all used false documents in the past, Mr Wilken said.
Mr Emmerson, representing seven of the men, told Siac there was no connection between the detainees and the London bombs.
There is no connection, suggested or evidenced, between those [London] attacks... and these applicants
Home Secretary Charles Clarke had not believed the men should be imprisoned when he imposed control orders on them in March, Mr Emmerson said.
"It's incumbent upon him to identify what has changed in relation to those particular applicants so that these conditions are no longer sufficient."
The Siac panel, headed by Mr Justice Ouseley, heard a report from psychiatrist Professor Michael Kopelman that H had "features of post-traumatic stress disorder" and had expressed "suicidal ideas".
Mr Kopelman also said that A had been suffering from depression while detained at Belmarsh high security prison, and to a lesser extent while on bail.
Jordanian Abu Qatada has been described by a Spanish judge as "al-Qaeda's ambassador to Europe".
He has been sentenced in his absence from Jordan to life imprisonment in relation to a series of explosions there.
Under the Human Rights Act, the UK cannot deport anyone to a country where they may face persecution.
Last month, an agreement was made between the UK and Jordan that deportees would not be persecuted.
But human rights groups say the agreement does still not guarantee safety after deportation.
Mr Wilken said a "memoranda of understanding" with Algeria would also be finalised next month.
The government is also in negotiations with nine other countries.
The hearing continues on Tuesday.