Come on guys think sensibly about this.
If you really want to know how the Police manage information there is a set of standards called MOPI, it's public information. You might also take a peek at BIP0008 which defines how evidential information has to be managed. If you provide information that convicts someone, that information must be held on file until there is no possibility of an appeal.
Not all information is held for twelve years, some less, some longer, that's just a default. When you call the non-emergency number, or 999, the details will be recorded just like calling a utility, on a CRM system. Some of that information may be passed on to the intelligence system, or other systems for actioning, just as you would expect. Because the Police are human beings, some of it gets misused or misfiled, deliberately or accidentally, just like any other organisations, but in the vast majority of cases it is managed correctly, and used correctly according to the processes the Police have in place, which again, may be wrong.
A lot of "detective work" is built up on pictures of events, which used to be done through a person called a collator who acted as the long term memory, now they also have intelligence systems which look at events reported by the public to determine patterns of criminal behaviour and so on, do you really want them to stop doing that. Remember that Tesco probably knows more about you that the Police do.
If you want to be anonymous, ring crime stoppers, they don't have to record your name, oh and 999really is for things that the Emergency Services can do something about now, if you see someone driving off in your car dial 999, if it's nicked from the station car park, it's not an emergency. Mind you it would help if there was a single non-emergency number, as how many of us actually know the non-emergency numbers for your areas, home, work....