It lists specific risks: 7 A nuclear attack "which would have a devastating effect on the UK"; 7 An attack on the London Underground using a small, unsophisticated, improvised explosive device; 7 A chemical or biological attack, for example, on the tube. "Biological or chemical attacks although potentially less devastating would lead to widespread public alarm and potentially many fatalities," the document says. A Home Office statement warns that because of its close alliance to America, Britain is vulnerable to a "nuclear attack, an attack on the London Underground of the type used in Paris in 1995... [or] a chemical or biological attack, for example on the underground". There is also the risk of a September 11-style attack involving hijacked airliners. Raised security standards have made such an attack more difficult, the document says, but "protection depends on their uniform application internationally". The 20-page document, placed before the court on behalf of the home secretary, David Blunkett, refers to intelligence warnings of further attacks and expresses the fear that if Osama bin Laden were killed, "the UK alongside the US will be a target for vengeance". It said the fact that Britain was a close ally of the US and that British troops were involved in the military action in Afghanistan and in seeking out Bin Laden made Britain potentially more vulnerable: "Whether he is killed or not Bin Laden's allies need urgently to re-establish their capability and intent in order to make up the ground they have lost since September 11: they will seek to do this through terrorist attacks. Al-Qaida supporters in Britain had played a role in four terrorist attacks foiled by police, the document disclosed. But it warns that efforts to deal with terrorists in Britain beyond these arrests had been "ineffective". "There remain in the UK a number of foreign nationals who are suspected of being concerned in the commission, preparation or instigation of acts of international terrorism." Security measures had been ineffective because the suspects arrested were released when the crown offered no evidence, or the suspects had chosen to leave Britain but continued to pose a threat, or because under human rights law they they could not be deported to countries where they might be ill-treated. The document says that the four terrorist attacks foiled by police and intelligence work were to have been carried out by "overlapping networks closely linked to al-Qaida". 7 In December 1999 a group of individuals in Jordan planned to attack a series of targets there frequented by American and Israeli tourists. 7 In the same month, Ahmed Ressam was stopped on the border between Canada and the US with a large quantity of explosive. He intended to attack Los Angeles airport. 7 In December 2000 a group in Frankfurt was arrested in possession of arms, chemicals and homemade explosive. 7 In September 2001 individuals in a number of European countries, including Britain, were arrested as they were preparing an attack against US interests in Paris. The document notes: "Activity in the UK formed essential building blocks for each of these frustrated attacks." ALSO Subject: Woolf and Mahathir Jail for sex offenders before crime ONDON: Britain's top judge said on Wednesday that some sex offenders who pose a threat to public safety might have to be incarcerated, even if they have not committed a crime. Civil liberties groups condemned the suggestion, and the government said it was not considering such a plan. "It may well be, and this is a matter of very great sensitivity, that we have got to think, for those who are persistent offenders, of having some form of protective custody," Lord Woolf, the Lord Chief Justice, told British Broadcasting Corp radio. "There may be a form of civil detention without having to prove a person has committed an actual crime," he added, "If they have committed the crime ... in some cases, in all cases, that's too late." Britain has been shocked by murder of 8-year-old Sarah Payne, who was abducted and murdered as she played in a field near her grandparents' home in July 2000. Roy Whiting, convicted December 12 of murdering her, had a previous conviction for the kidnap and indecent assault of a 9-year-old girl. Whiting served just over half his four-year sentence for that crime, and refused a prison program designed to rehabilitate sex offenders. Woolf conceded that protective custody would be a huge infringement on the individual's rights.