The Home Office has issued no such guidance to the police.
The PNC retention guidelines issued by the Association of Chief Police Officers include an exceptional cases procedure. In accordance with this, it is for individual chief police officers to use their discretion to decide whether to amend or delete information placed by their force on the police national computer (PNC) and the national DNA database (NDNAD). In exercising that discretion, they may make different decisions in respect of information held on the different systems.
The police national computer (PNC) is an operational tool and is not designed to produce the information requested. To obtain the information would incur a disproportionate cost.