How many double check valvs in new build

[Drew1000]

I am currently building a timber frame house in Scotland so Scottish Water regulations.  Can anyone advise how many double check valves I need to fit and where.  I am aware I need (at the incoming mains) an isolator, double check valve and drain point which I have already installed.  I have heard conflicting reports that I need them at every appliance ie dishwasher, washing machine, showers etc.  Others say just at the incomer.  Any one know the definitive answer to the question.  Regards 

[ProDave]

No just the one on the incoming.

 

and one on the site stand pipe.

 

And one on the feed to the static caravan.