Hi,
Re Police whistles, from my own experience I can tell you that Cleveland Constabulary (now known as Cleveland Police) issued the following whistles from 1979 to C.2000 when they were no longer issued.
All conform to the WW2 ARP pattern.
The force never had its name stamped on the whistles.
Marked examples known are;
A.R.P. J. Hudson, Barr St. Birmingham.
The Metropolitan. Made in England.
The EMCA City Whistle. Made in England.
The ACME City. Made in England.
SONDICo. made in India.
Vosper