I would make some discrete enquiries with the health & safety executive. As you know, I am an Ambulance Officer and we are subject to the same regs as the Police.
The standard of high viz markings on vehicles and clothing etc is subject to conditions of the roads served.
For example, the infamous "battenburgh" markings on vehicles are only a requirement on vehicles that have to stop on high speed roads such as motorways, dual carriageways etc. (Where normal vehicles are not allowed to stop) Hence the "hobbyists" (meant in a kind context) such as the voluntary ambulance services, together with private ones do not need theses markings. (But they would not have so much fun without them eh???)
Having said that, any vehicles that do adopt them have to then comply to STRICT specs.
It is a similar situation with high viz. You will notice all the Motorway organisations including the Emergency Services, breakdown & motorway maintainance personell have to comply with the higher specs required for their environment. But have a look at the average Council employee, or the utility workers and you will see some still wearing sleeveless vests which were "outlawed" for us some years ago.
I fail to see why the Police are insisting on you using hard earned funds to update to the latest "fashion," other than perhaps they wish to use you on motorways etc ??? in which case surely the onus would be on them to assist you???
I was a member of the now defunct Gwent Ambulance Search & Rescue team and did all my training with Morlais MRT. (Now Central Brecon)
I now restrict my skills to the Gwent Cave rescue team, where there are DEFINATELY no artic lorries thundering by, hence, no Hi viz!!!
:-))))