There's an odd story over on the Beeb at the moment about a chap who infiltrated a morning meeting at the West End Central police station dressed as a copper. He strolled in with a real police officer who was taken in by the uniform which was authentic right down to the pepper spray and handcuffs.
It is understood he attended a morning meeting on 11 November which covered information about bomb threats. But his cover was foiled when another officer became suspicious. He was later arrested for impersonating a policeman. Police also arrested him for possession of a firearm, thought to be pepper spray, and bailed him until January 2006.
If you fancy having a go at seeing what goes on in your local nick without the bother of joining the force or getting yourself arrested then you'll need to befriend an expert like the chap who runs London Bobbies dot com. It's more of a site for collectors of police memorabilia, but has gone some great information for the casual browser (despite not being updated in a while and being a refuge for too many animated gifs):
Now you may wonder why the Metropolitan Police Officer looks like he has slept in his uniform, this photograph would have been taken at the turn of the last century and at this time Standing Orders for officers were that they were to be in Uniform at ALL times (except when sleeping) and the Duty band you can see on his Left cuff showed if he was on duty or not, if as in this case he was wearing it, then he was on duty. Officers at this time were rarely permitted time off or leave.
There's also more information on there than you'd ever need about helmets...