Police or Forensic Psychology work experience?Watch
[Idk if it's relevant but I live in London]
For over 18s, some potentially relevant work experience could include being an Appropriate Adult, detention advocate, working voluntarily doing admin or support work with the police, Victim or Witness Support services, drug & alcohol helplines, all sorts (although even then it's very difficult to get into).
Under 18...there's possibly things like Police Cadets if you're interested? Have a look at do-it.org - you can search specific locations or areas of interest, so you might get some more ideas.