Like the proverbial Irishman who was asked for directions, Charles Clarke, the home secretary, protests that he would not have started from here in the first place. Mr Clarke has suspended our rights to freedom from imprisonment without trial in order to detain a few foreign terrorists. These ancient liberties, treasured under the name habeas corpus, should not be interfered with lightly.But the home secretary is hoist by his government’s petard. It chose to incorporate the European convention on human rights into British law. Under its provisions, judges in the House of Lords have ruled that powers to detain 11 foreign terrorist suspects in Belmarsh prison were incompatible with the convention as they were “disproportionate” to the threat and applied only to foreigners. Mr Clarke has responded by taking powers to keep all terrorist suspects under house arrest outside prison. It is a power that applies in equal measure to Britons as well as foreigners.

Mr Clarke is doubtful of the legality of his latest measure. He knows it may be struck down by the judges. Like his predecessor David Blunkett, he might have preferred that the Guantanamo quartet had never been returned to Britain although that, too, was the policy of his government. He must curse the intelligence agencies, Home Office officials and liberal asylum laws for allowing Islamic terrorists free passage into Britain for two decades, despite repeated warnings from France. Such people turned the capital into “Londonistan”, a hub of Al-Qaeda operations in Europe. He may even damn the new generation of liberal judges that tears up his laws although it was Labour that used to sneer at “reactionaries” on the bench. But here he is and here they are. We have to suffer the consequences.

Despite this there is a case for detention without trial for the simple reason that it works and it protects innocent civilians. Foreign nationals were interned during the last war. There were many injustices but it was deemed a necessary emergency measure. Two IRA campaigns were defeated by the detention of terrorist suspects without trial with the co-operation of the Irish republic. It failed during the last Troubles because London was at loggerheads with Dublin. Internment is an extreme measure. Mr Clarke can argue that the threat to our security from Al-Qaeda is extreme. He is probably right, but is his course wise? First, he should re-examine the case for bringing suspects to trial. Phone tap evidence is inadmissable in our courts. The authorities have long argued that they need to prevent suspects knowing their sources. But now even MI5 has given up arguing that one. European governments use phone tap evidence to jail terrorists all the time. Examining magistrates in Europe are also given wide powers to detain suspects as long as it is understood that a case will eventually be brought to trial. Maybe we have something to learn from practices that at least avoid the ceaseless round of court battles led by human rights lawyers.

Second, the home secretary and his colleagues should accept their lack of credit in the bank of public opinion and do something about it. By its over- reliance on spin, its corruption of the civil service and its mendacious presentation of evidence for weapons of mass destruction in Iraq, the government has lost its reputation for honesty. Without trust, many people simply will not believe that the Home Office has a case for detaining suspects when it fails to produce evidence. The government also has previous convictions for constitutional vandalism. The House of Lords and the office of lord chancellor have been kicked around like footballs.

The concept of “separation of powers” seems alien to ministers. Mr Clarke must belatedly try to build a consensus for security measures outside the new Labour bunker. The public needs protecting but the question is: at what cost? Mr Clarke might consider another lesson from Northern Ireland. When the jury system broke down under intimidation, non-jury trials were enacted. If as an emergency measure the rules of evidence need to be changed to help the prosecution, then judges not politicians should preside over the process.