The investigation, which comes on top of an initial investigation into the trust's maternity care, was declared as the Ockenden Maternity Review said its findings would be delayed by nine months after up to 300 additional cases were discovered.

Assistant chief constable Rob Griffin said: ‘I can confirm that following consultation with HM Coroner and the Donna Ockenden review, a difference in the number of referred cases was identified.

‘With the agreement of all involved, NUH appointed someone to review some of these cases. That person created a digital file, in relation to their work. Along the journey that file was found to have been deleted and NUH alerted Nottinghamshire Police to this fact.

‘The file has been recovered and has since been provided to Nottinghamshire Police. The fact the file had been deleted has not impacted on the investigation, nor on any of our decision making in Operation Perth.

‘Nottinghamshire Police will however investigate how that file came to be deleted and although this investigation will be separate to Operation Perth and will be conducted by the force's cyber and digital investigation team, I will have oversight of it.'