The police keep every interaction with you on record, but much of this is inaccessible to the general public. They keep information even if you were never charged, or were acquitted, or otherwise totally exonerated at any stage. The police are not very good at admitting they were wrong, so they won't delete anything because they always assume/believe you are guilty and just can't prove it. Presumption of innocence in this country is a myth.
For this same reason, if you ever have to do an enhanced DBS check, there is a section where the Chief Constable can add any information "that they deem relevant". In real terms, this means ALL information that they have ever had on you, including rumour, gossip, false accusations, etc. Even stuff that you were never even aware of.