Boris Johnson has admitted he has no idea how many criminal cases have been damaged by a massive Home Office data loss.
The Prime Minister said "we don't know many cases might be frustrated as a result of what has happened" after being challenged by Labour leader Keir Starmer.
An estimated 213,000 offence records, 175,000 arrest records and 15,000 records on people were potentially incorrectly deleted as a result of a defective code.
At PMQs, Mr Starmer said: "It's 10 days since the Home Office mistakenly deleted hundreds of thousands of vital criminal records, including fingerprints, crime scene data and DNA records.
"So can the Prime Minister tell the House how many criminal investigations could have been damaged by this mistake?"
Mr Johnson replied: "The Home Office is actively working to assess the damage and, as he will know from the urgent question in the House a few days ago, they believe that they will be able to rectify the results of this complex incident and they hope very much that they'll be able to restore the data in question."
Pressed on how many criminals had their records deleted, Mr Johnson said: "We don't know how many cases might be frustrated as a result of what has happened.
"But I can tell him there are 213,000 offence records, 175,000 arrest records and 15,000 person records currently being investigated because they are the subject of this problem."
But Mr Starmer pointed to figures from the National Police Chiefs Council, which said 403,000 records may have been deleted from the Police National Computer.
He said: "This isn't just a technical issue, it's about criminals not being caught and victims not getting justice.
"This letter makes clear that it includes data from criminals convicted of serious offences, it has impacted live police investigations already and it includes records, including DNA marked for indefinite retention following the conviction for serious offences."
Mr Starmer demanded to know why the Government had not answered basic questions, 10 days after the incident came to light.
The Prime Minister said the police are working "round the clock" to retrieve the data.
The records were deleted accidentally from the Police National Computer by mistake during routine maintenance, Policing Minister Kit Malthouse confirmed at the weekend.
