The Home Office's Criminal Records Bureau wrongly denounced or cleared more than 1,500 people in the last year, almost three times as many as the previous 12 months.
The embarrassing figures have emerged ahead of a massive increase in the number of people who will be subject to background checks when the new Vetting and Barring Scheme comes into force in October.
In the 12 months to March 31 this year the CRB made 1,570 errors. The errors included stigmatising innocent people, wrongly listing more serious offences, and mistakenly clearing criminals to work in sensitive jobs.
The figure compares to 680 errors during the previous year.
The Home Office said: "For the first 11 months of 2008-09 the CRB's accuracy rate exceeded the previous years.
"However, a dip in the quality in the final month brought down the overall figure. Disclosure quality and accuracy is heavily reliant on the information supplied by the individual and is subject to fluctuations."
A Home Office spokeswoman said there was no particular reason why there were about 1,000 errors in March. "There are fluctuations," she said.
The department is preparing for the launch of the Independent Safeguarding Authority (ISA), the centrepiece of the government's response to the Soham murders inquiry, and the agency responsible for the Vetting and Barring Scheme.
The CRB will act as one of the ISA's main sources of data to vet 11 million adults in a much broader range of jobs and volunteer roles that are currently scrutinsed.
The CRB last year ran 3.9 million checks, up 500,000 on the previous year. ®