More than 400,000 fingerprint, DNA and arrest history records have accidentally been deleted from police databases because of "human error" and "defective code", the policing minister Kit Malthouse has said.
Police leaders are concerned that the chaos may cause them to hold data they should have legally deleted.
Mr Malthouse said problem happened during routine maintenance of the Police National Computer earlier this week.
He said: "Unfortunately down to human error, some defective code was introduced as part of that routine maintenance earlier this week and that's resulted in a deletion of some records and that's currently under investigation.
"We have already put a stop to the problem so it can't reoccur.
"And we are now working very quickly with policing partners and within the Home Office to try and recover the data and assess the full extent of the problem."
Pressure is mounting on the home secretary, Priti Patel to give a full account of the blunder affecting the police national computer (PNC), which is run by the Home Office.
A letter sent to senior officers on the National Police Chiefs’ Council (NPCC) on Friday from deputy chief constable Naveed Malik, lead for the organisation on the PNC, outlines the scale of records affected:
“In PNC approximately 213,000 offence records, 175,000 arrest records and 15,000 person records have potentially been deleted in error.
"In terms of understanding the potential linkage between records, a one-person record can have multiple arrest records and one arrest record can have multiple offences linked to it.”
Technicians are also scrambling to recover tens of thousands of fingerprint records, according to the deputy chief constable’s letter, which says that “30,000 fingerprint records and 600 subject records have potentially been deleted in error”.
The deletion has also caused chaos with the visa process. Applications, which are checked against the PNC, were suspended for two days but have now resumed.
A spokesperson for the NPCC said: “We are aware of an issue with the PNC and are working closely with the government to understand the potential operational impacts.”
Former Cumbria police chief Stuart Hyde said the loss was a "risk to public safety and a risk to the safeguarding of vulnerable people across the country".
He told the BBC: "In terms of the risk this creates clearly some of those people may be involved in subsequent offending and could only be identified through either fingerprints and DNA when they were subsequently brought to light.