Nearly 1,500 people have been falsely accused of being criminals by the criminal records bureau (CRB), it has emerged.
The mistakes by the Home Office resulted in many people being turned down for jobs or places at university because of the errors.
The government said the mistakes were regrettable but said it made "no apology for erring on the side of caution".
The errors happened as a result of "mismatches" which happened when the CRB was carrying out checks on people applying for positions of trust in jobs such as teaching, according to the Mail on Sunday.
When an individual's details were very similar to a convicted person's data on the police national computer, this led to a case of mistaken identity.
The Home Office said 90 per cent of the errors were sorted out within 21 days, and only 0.03 per cent of the total number of checks the agency made were wrong. Checks made by the CRB last year prevented 25,000 unsuitable people being recruited, it said.
A spokesman said: "The criminal records bureau's first and foremost priority is to help protect children and vulnerable adults by assisting organisations who are recruiting people into positions of trust.
"These cases are clearly regrettable, but represent a tiny proportion of cases - 0.03 per cent of the nine million disclosures issued by the CRB since it began operating in March 2002.
"We err on the side of caution in these rare cases precisely because it is vital to ensure that the disclosure individuals do not fraudulently try to claim they have no criminal convictions when in fact they have."
However, shadow home secretary David Davis warned: "The refusal of ministers to face up to their own responsibility and to allow this dreadful practice to continue is not just a failure to do their duty; it is a willingness to perpetuate a serial injustice."