The Home Office clashed openly with judges on Monday when it criticised a decision to free on bail within days the radical Islamist cleric Abu Qatada, who is accused of posing a grave threat to British national security.

The decision by Mr Justice Mitting will see Abu Qatada, once described as Osama bin Laden's righthand man in Europe, walk out of Long Lartin maximum security prison in Worcestershire after more than six and a half years in detention without trial - the longest period in modern times.

The special immigration appeals commission (Siac) has imposed some of the most draconian bail conditions seen since 9/11, including a 22-hour curfew, but this did little to assuage the anger of the Home Office ministers or politicians from all parties at the decision.

The clash takes the battle between politicians and the judiciary into new territory as Abu Qatada is a major international terror suspect. He was first detained without trial in Britain under the quashed Belmarsh regime nearly a decade ago, in October 2002.

The decision taken by the high court judge at Siac follows the ruling by the European court of human rights that he could not be deported to Jordan because he would face a "flagrant denial of justice" - a retrial based on evidence obtained through torture. Abu Qatada had been detained under immigration laws for the past six and half years pending his deportation to Jordan.

A Home Office spokesperson said he should remain in detention: "This is the argument we made in court and we disagree with its decision. This is a dangerous man who we believe poses a real threat to our security and who has not changed in his views or attitude to the UK."

The Home Office said it will consider an appeal against the European court's ruling. It will also continue a fresh attempt to secure diplomatic assurances from Jordan that Abu Qatada will not face a trial based on torture-tainted evidence.

The British ambassador held two meetings last week with the Jordanian authorities to try to open talks on the issue.

But the decision angered both Labour and Conservative backbenchers. The former Labour home secretary David Blunkett said the decision had left the government facing a very real difficulty: "It is an unholy mess. We are left in the absurd position of not being able to remove a man even though everyone accepts he won't be tortured, not being able to keep him in prison because his human rights trump the protection of the British people, and a government that has watered down control orders so that they are more lax than was previously the case."

The Conservative backbencher Dominic Raab echoed Blunkett's anger: "This result is a direct result of the perverse ruling by the Strasbourg court. It makes a mockery of human rights law that a terrorist suspect deemed 'dangerous' by our courts can't be returned home, not for fear that he might be tortured, but because European judges don't trust the Jordanian justice system."

The bail conditions set down by Mr Justice Mitting are draconian, comprising a 22-hour curfew rather than the "overnight residence requirement" specified in the coalition's replacement for control orders. They include an electronic tag, MI5 vetting of all his visitors except for immediate family, and monitoring of his communications. The delay in his release is to allow the security services to check the proposed bail address and organise their surveillance operation.

In his ruling, the judge said that although the six and half years Abu Qatada had been detained under immigration powers was "unusually long", he agreed with the home secretary that it was also lawfully justified. However, he added: "The time will arrive quite soon when continuing detention or deprivation of liberty could not be justified." The Siac judge warned the home secretary, Theresa May, that Abu Qatada's "highly prescriptive" bail terms would be relaxed after three months if there is no "demonstrable progress" made with the Jordanians.

The bail conditions mirror those set in 2008 when he was released for six months before being returned to prison on unspecified national security grounds. The judge said the risks to national security and of absconding in the case had not significantly changed since then.

During the one-day bail hearing, Edward Fitzgerald QC, representing Abu Qatada, argued that his detention had gone on too long to be reasonable and there was no prospect of the detention ending in any reasonable period. Even if new diplomatic assurances were secured it would only trigger a new round of litigation in the English courts."There comes a time when it's just too long, however grave the risks," said Fitzgerald.

The shadow home secretary, Yvette Cooper, said May had to explain urgently what action she was taking on the national security implications of the ruling. "Abu Qatada should face terror charges in Jordan, and the home secretary needs to urgently accelerate discussions with the Jordanian government to make that possible," she said. The home secretary also had to spell out the counter-terror safeguards that will be taken to lower the national security risk.

The security services have never disclosed the actual cost of mounting round-the-clock surveillance operations on terror suspects such as Abu Qatada but it does have serious implications for their resources.

Abu Qatada, whose real name is Omar Othman, 51, featured in hate sermons found on videos in the flat of one of the 9/11 bombers. Since his original detention in October 2002, every attempt to deport him to Jordan has been frustrated. The law lords ruled three years ago that he could be sent back but the Strasbourg decision overturned that ruling.

Abu Qatada release: Home Office Fury As Judge Frees 'Bin Laden Aide'

looking for root causes .....

Why cannot Abu Qatada, described as a dangerous man who poses a grave threat to Britain's national security, be charged with criminal acts and put on trial in a British court? There are a number of possible answers.

One is that embarrassing information about MI5 and the Met police would come out in court. When Qatada came to the UK in 1994 as a refugee, MI5 believed he was not dangerous. Comments by the well-known Spanish judge Baltasar Garzón describing Qatada as the "spiritual head of the mujahideen in Britain" were dismissed by British security and intelligence sources as overblown.

MI5 was sharply criticised by the special immigration appeals commission (Siac) in 2007 for misjudging Qatada, who had argued in one of his appearances before the commission that MI5 "knew the sort of views which he was expressing and took no steps to stop or warn him, to prosecute him or prevent his fundraising for groups which are regarded as terrorist groups ... or for training in Afghanistan".

According to the Siac judgment, that inaction was based upon "an erroneous assessment of the damage which the preaching and propagating of radical views could do within this country and elsewhere".

MI5 later came to realise that Qatada's preaching and incitement was potentially dangerous and harmful. It approached him and tried to persuade him to tone down his jihadist talk, at least insofar as it was addressed to audiences here.

Qatada appeared to dismiss MI5's approaches and in 2001 he began trying to justify suicide attacks. That year police found £170,000 in cash in his home, including £805 in an envelope labelled "for the mujahideen in Chechnya". Richard Reid, the failed shoe bomber, and Zacarias Moussaoui, both jailed on terrorism charges, were said to have sought advice from Qatada. Some his sermons were found in a Hamburg flat used by some of those involved in 9/11.

One view expressed in Whitehall is that there is insufficient evidence to convict Qatada at a trial. Qatada was not a bombmaker, nor did he ever plan to plant bombs, it is argued. His role was that of a radical preacher, to influence by words, not deeds.

Yet he did not mince his words. It is not as though the evidence is confined to telephone taps, the product of which is still inadmissable in criminal trials in the UK. In 2007 Siac ruled that Qatada had "given advice to many terrorist groups and individuals ... His reach and the depth of his influence in that respect is formidable, even incalculable." A year later the Siac judge, Mr Justice Mitting, said Qatada "expressed very forcefully his views direct to me" and he "has shown no inclination of any change in attitude".

Well before then, a plethora of anti-terrorist laws had been passed to cover a very wide range of offences, including incitment. The 2000 Terrorism Act made incitment to terrorism overseas a criminal offence.

MI5 and the police might not have welcomed a trial because it would have resurrected the circumstances surrounding the seizure by the CIA of two British residents - Jamil el-Banna, a Jordanian national, and Bisher al-Rawi, an Iraqi - in Gambia in 2002, leading to their rendition to Guantánamo Bay. MI5 documents disclosed in court describe the agency's attempt to recruit Banna as an informer eight days before he flew to Gambia for a business trip. Rawi had also helped MI5 to obtain information about Qatada. Banna had prayed in the same mosque as Qatada when they lived in Peshawar, Pakistan. Banna, Rawi and Qatada later prayed in the same mosque in London.

Lawyers familiar with the long-running case say the government was determined to go down the deportation route, one that would have avoided any potential embarrassment or problems with evidence emerging in court here. It was an easy option, it was thought. Instead, because Jordan has refused to promise it would not use evidence obtained by torture in his trial there, a serious national security threat remains here, convicted of no crime.

Why Has Abu Qatada Not Stood Trial In The UK?