As an aside, this specific problem seems like something there could be a strong cryptographic solution to. eg rather than just deleting records, they could enc

As an aside, this specific problem seems like something there could be a strong cryptographic solution to. eg rather than just deleting records, they could encrypt them first with a public key where the private half is owned by a third party such as the information commissioner (https://ico.org.uk/ https://ico.org.uk/) and then archive them. If at a later date they find they need them back they request a decryption and give their reasons. If the ICO thinks the reasons are valid (ie the police have the right to have the data and therefore should not have deleted it), then they decrypt, but otherwise the police don't have access to the data. Usage of the private key could be subject to an audited break glass procedure to prevent abuse.