Britain's own Guantánamo

Last week an Old Bailey jury stood up to be counted and acquitted a young Muslim, Cerie Bullivant, of seven charges under the Prevention of Terrorism Act 2005. However, he is still having to conduct his life under the non-criminal control-order regime. Were you to be issued with such an order, you would know only that it is asserted that you are suspected of involvement in terrorism. Any evidence remains secret. Your pattern of existence would be instantly recognisable to former victims of house arrest in apartheid South Africa: intrusive obligations dominate your life and that of your family. Any breach - being late in daily reporting at a police station, or failing to make a monitoring call in the night - becomes triable before a jury as a terrorism-related crime. The jury is told that you are a suspected terrorist but is not told why. How can you, an innocent person, fight the imputations of the secret order in such a clumsy, asymmetrical criminal trial? How can you explain that your breaches were born of despair at the unendurably intrusive injustice of false accusation?

The most elementary requirement of legal certainty demands that you know the case against you. And yet considerable numbers of young men, and some women, are being held in our prisons without any idea of why they are there. They are detained under yet more provisions, for the present deemed lawful, which either forbid or demand no meaningful explanation being given to the accused. The concept of secret evidence and accusations so vague and undefined as to be meaningless has now bedded down in our system of justice.

Men await deportation to torturing regimes on the basis of accusations concealed from them in the Special Immigration Appeals Commission. They are held with others facing extradition, where the requirement by the UK of provision of a prima facie case has been abandoned in favour of a fast-track procedure, without evidence, designed to effect rapid delivery of suspects to the US. Worryingly, within the "ordinary" criminal process, many defendants now face charges of such vagueness and uncertainty that, even after a trial, in many cases after conviction, they still have no understanding of why what they have done has been ruled criminal.

Defendant after defendant has discovered that a long-forgotten internet search has left an indelible record sufficient for a conviction under the profoundly disturbing section 58 of the Terrorism Act 2000, which allows prosecution for simple possession of an item likely to be useful to terrorists, and carries a sentence of up to 10 years' imprisonment. While the record of use remains permanently, no equivalent reconstruction is available or even required of the mindset of the user at the time. The common elements in each conviction have now become familiar: the defendant had not the slightest idea that such possession was inconsistent with the right to freedom of thought; was not remotely involved in any terrorist activity; and was Muslim.

To be blunt, as most of such prosecutions to have gone through the courts have succeeded, there is now the bleak prospect of imprisonment for thousands of young people, all Muslim, who have similarly accessed the internet prompted by an interest - shared with millions of their contemporaries around the world, Muslim and non-Muslim - in the workings of political or radical Islam. Additionally, possession of the Channel 4 film Road to Guantánamo, or 21st-century Crusaders, a compilation of documentaries from the BBC and elsewhere, is currently being held to demonstrate "radicalisation", a condemnation as conveniently imprecise as the label "subversive" used in the postwar McCarthyite witch-hunts in America.

In the face of a succession of questionable convictions, we now see a new and disturbing phenomenon whereby more than one innocent defendant, unable to comprehend the accusation levelled, yet terrified at the prospect of inevitable conviction, insists on pleading guilty in an attempt to avoid sentences that become ever more severe.

Such increasing contamination of the legal process, capitulating to an insatiable executive appetite for secret hearings when the spectre of national security is invoked, brings about a distortion of what should be the central purpose of the criminal process: achieving justice through predictable certainty and clarity. This week's returnees from Guantánamo faced secret hearings no more unjust than ours.

For the accused, such dysfunction brings even more acute danger. In the television drama Britz, a young woman, the subject of a control order and overwhelmed by its injustice, hangs herself. In the real world in recent weeks, three young Muslim men arrested and imprisoned in Belmarsh for breaches of control orders have made similar attempts on their lives. One of these was Cerie Bullivant. A different, less clear-sighted jury might so easily at his trial have left him for life with seven convictions for activity related to terrorism. Instead, their verdict that his every breach, including absconding, was reasonable in the face of the crushing effects of a secret accusation by the state, delivers the most authoritative possible verdict on the legitimacy of these laws and gives us a moral as well as legal basis for demanding change on behalf of our many fellow citizens at daily risk of such brutal injustice.

Gareth Peirce, a human rights lawyer who represents Cerie Bullivant.