One issue is whether these people should be in Britain at all. Some people point out that they have no connection with Britain and in some cases have committed criminal offences. Yet that be as it may, they are here and have nowhere else to go. (Sending somebody to country where they will be tortured and/or killed is not an option)
The second issue is that while they are in Britain, should they be treated in this manner. Here my argument is clear: if they have committed a crime, then they should be prosecuted in open court for it; if not, then they should be free to work and earn money for themselves and their families.
My own hunch is that these are desperate and/or pathetic people who represent a threat to nobody in Britain. Rather than admit there is nothing against these people, a wholly immoral British government is playing secrecy/national security card, merely to hide the lack of evidence; thereby hoping to avoid a loss of face.