John Reid faces intense embarrassment after admitting that a terrorist suspect vanished within days of being issued with a control order that was meant to restrict his movements.
The authorities have now lost track of three of 18 men they believe to be such a serious threat to security, either at home or abroad, that they have to be constantly monitored.
In a further damaging blow to the embattled Home Secretary, a Home Office report raised serious questions over border controls at major airports. It warned that immigration officers felt under "intense pressure" to allow foreign travellers into Britain, even where there were doubts over their status.
Mr Reid's efforts to get a grip on his department were set back last week by the disclosure that details of 27,500 convictions of Britons abroad were allowed to pile up in the Home Office without being entered on the national police computer.
Yesterday, Tony Blair expressed confidence that Mr Reid, who held what he called the "toughest job in government", would turn around the Home Office.
Within hours, however, the Home Secretary admitted that another terrorism suspect was on the run despite being on a control order, which required him to surrender his passport, live at a specified address and report daily to police. He is understood to be a Manchester man who had recently become radicalised and was suspected of planning to travel to Iraq to join the insurgency against Western troops.
Mr Reid said: "The individual is not believed to represent a direct threat to the public in the UK at this time."
Control orders, which can amount to virtual house arrest, were introduced two years ago after the policy of indefinite detention was thrown out by the courts. Eighteen control orders have so far been issued, but their shortcomings were exposed by the disappearance of an Iraqi man last August and of a UK national the following month. Both are still missing despite intensive police manhunts.
Home Office sources said that the latest man to abscond was at the "low end" of the control orders and argued there was no need for public alarm.
Meanwhile, Home Office research has discovered that immigration officers sometimes wave passengers through passport control because of staff shortages. It disclosed that staff at Heathrow and Gatwick airports were encouraged to grant "borderline" cases if in doubt. The Home Office report said: "At certain times of the day, when a lot of flights come in at the same time, control can become extremely busy.
"If this coincides with staff shortages, immigration officers can feel under intense pressure to deal with passengers more quickly than they would like, and sometimes to let passengers through without making further inquiries."
The report added: "Some immigration officers described rare occasions when, due to staff shortages, they had been instructed by chief immigration officers not to hold up any passengers at all."
David Davis, the shadow Home Secretary, said: "These disgraceful disclosures over control orders and border controls is more evidence John Reid is failing to protect the public."
* Five offenders convicted of serious crimes abroad are still working in jobs in Britain which required them to be vetted by the Criminal Records Bureau, the Home Office said last night. However, none of them had convictions for sexual and/or violent offences, it added.