If you are a civi then the H&S (SHEFF) will vapourise you if you don't have one. In the Mil, you should be more worried about bullets (or bl-unties) so Hi-Viz vests aren't needed - unless - you have a head shed that has no balls!!
A well known Hampshire base had them, then a man took over and they don't any more.
Pooh-Bar to the PC brigade!!!