All rather irrelevant when at Leuchars if you go to supply to ask for said vest as aircrew the response is "Sorry Sir aircrew aren't scaled for a Hi Vis Vest"
I suggest you pop back to clothing stores and ask them to show you the 'supplementary safety equipment scales' which are located towards the back of the clothing scales. Items such as hi-viz vests are issued 'as required' and no one is specifically scaled for them as they are issued to task.
Safety equipment is the one item in clothing stores that everyone can make a case for and if you get any grief get your station H&S bod on their case.