The case against an Algerian national facing deportation from the UK under terror laws does not stand up to scrutiny, a court has heard.
Some of those detained have been held at Belmarsh in the past
Keir Starmer, lawyer for a man known as T, told a Special Immigration Appeals Commission (Siac) bail hearing how he had lived freely in the UK since 2001.
But the government said T was "closely associated" with Islamist extremists.
He is one of 10 suspects, including radical cleric Abu Qatada, detained since August pending deportation.
All 10 are applying for bail and the Siac panel is expected to announce a decision next week.
The court heard how T was an asylum seeker who came to the UK in 2001 and has two children who were born in Britain.
The government claimed he had lived at the same address as one of the other nine detainees in early 2001, and had received terrorist training in Afghanistan.
But Mr Starmer told the Siac judges that the government must have known about these allegations for "a considerable period of time", yet his client "simply wasn't considered a risk".
"The submission that there are no conditions that could now be imposed on T to ensure he was not a risk... simply doesn't stand up to scrutiny."
Siac judges also heard the bail application of suspect I, another Algerian, on Tuesday.
He is accused of raising funds for terrorist groups and helping Islamists travel to the UK, but Mr Starmer said the risk from him had always been "satisfactorily managed".
The 10 were taken into custody on 11 August as part of a crackdown on suspected terrorists 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.
Home Office barrister Sean Wilken told the judges last week that all of the 10 were "dangerous men".
The UK does not deport to countries where people may face persecution, but ministers are seeking guarantees from a number of countries that the detainees will not face torture or the death penalty on their return.