Isn't that what some MP is suing about? He apparently made a quip about Trans folk, a complaint was made and the Police investigated. They decided it didn't breach the criminal threshold but they recorded the incident. Later, the police referred to it with a number - effectively, the guy was now on a list. The police have also said they will investigate every complaint and presumably record the results. No idea what is being done with this list but as it's a public record, I presume other agencies will be able to access it.