Non-return valves

[denis567]

I posted this question a while ago under Gardening, but I wonder if anyone has a link to refer to the legal aspect.
At my old address the outside garden taps were fitted with non-return valves, but at my new address they do not have these valves.
I got a reply saying that all stop taps are fitted with one-way valves, so am I right in thinking that if the garden taps are fitted after the main stop tap, then a non-return valve isn't required. Thanks