How do I get my personal information and details removed from the Police's databases?
The Police's power to retain personal information (eg. your DNA or fingerprints) depends on your particular circumstances. If you are an adult and have been arrested or charged with (but not convicted of) Section 14/obstruction of the highway offences which have been discontinued, then any personal information must be destroyed unless you've previously been convicted of a recordable offence that is not an “excluded” offence (in which case the information can be kept indefinitely). Section 14 is a recordable offence but Obstruction of the Highway and Breach of the Peace are not. A "conviction" for these purposes includes cautions, warnings/reprimands and out of court disposals.
In order to have your details destroyed, you would need to fill in an application for destruction, set out in detail (with example applications) here: https://www.acro.police.uk/Services/Record-deletion. Again, you can do this yourself or talk to one of the law firms listed above to get their assistance with it (especially if you're planning to bring a claim for false imprisonment).
Those who have already been charged can also get their personal information which was published by the Police removed from their website. You can either write to the Police about this or consult one of the lawyers for further guidance.