Non Return Valves on everything?

My house is 1975 build and over the years like millions of others I have DIY’d new shower room, bathroom, kitchen sinks, outdoor taps, CHtg mods etc etc.

Various forums mention the use of non-return valves on outside taps, wc’s etc and I presume the water regs have changed over the years. I get the impression that current regs call for NRV’s on virtually everything connected to the rising main?

Could someone please summarise the requirements when replacing items and clarify any areas where regulations require retrofitting of such devices.