Home Office figures on major policy areas are "not up to scratch", the department's most senior official said.
Almost 20 per cent of statistics used by the department were not reliable, Sir David Normington, the permanent secretary at the Home Office, told MPs.
He apologised for supplying inaccurate data on anti-social behaviour disorders (ASBOs) and said that, as part of the Home Secretary's review of the department, which uses statistics on crime, immigration, prisons, asylum and anti-social behaviour to underpin national policy, 160 sets of data had been analysed.
"We have given them a star rating according to assessment of their reliability from 'three' to 'zero'. We are looking actively at the 30 data sets which we didn't think were up to scratch," he told the Commons' all-party Public Accounts Committee.
Sir David did not specify if the inadequate statistics were found in one main area that the Home Office is responsible for, or across several areas, but the department is expected to announce measures to improve immigration statistics today.
Ministers also came under pressure at Home Office Questions over the fiasco that allowed 27,500 case files detailing offences committed abroad to gather dust. The Conservatives joined the Liberal Democrats in demanding an independent inquiry into why the details were not entered into the police national computer.
David Davis, the shadow Home Secretary, said it was "entirely inappropriate" for it to be left to civil servants to investigate the mistakes. Tony McNulty, the Policing minister, said the Home Office was "getting to grips" with the problem by launching an inquiry and raising it internationally.
Meanwhile, the Home Secretary warned that the struggle to defeat the growing threat from al-Qa'ida could last almost half a century. John Reid drew a parallel with the "battle for hearts and minds" between the West and the Soviet Bloc from the mid-Forties to the fall of the Berlin Wall in 1989. He told the Commons that the first known British al-Qa'ida plot was hatched in Birmingham in 2000 and, since then, the threat from Islamist extremists had "grown apace year by year".
Mr Reid said: "The threat from international terrorism is seamless and is no longer easily divided into foreign, defence and domestic affairs. Our counter-terrorist campaign will need to be seamless, integrated, politically driven, forward-thinking, dynamic and have at its heart the recognition that, above all, this is a battle for hearts and minds, a struggle of ideas and values."
* Mr Reid signalled the Government would sign the European Convention against Human Trafficking. It will oblige Britain to give victims help with housing, medical treatment and legal advice. An estimated 4,000 women were smuggled into Britain in 2003 to work as prostitutes.Reuse content