I am not sure that is the case. As far as I can recalll you merely need one open pipe per 50 meters or something of drain, to vent positive pressure.
Air valves can be then added wherever neded to prevent siphoning.
Well my parents house in 1953 had exactly that arrangement.
BCO's can be surprisingly ignorant.
Mine was not aware that
- if you use guttering you must comply, but there is no requirement to use guttering at all! Merely that there mus be wome means of stopping water getting onto your walls..
- you don't need safety glass in a multi-paned French window (leaded) and indeed, it can't be realistically cut that small either.
In every case the regulations section begins with a 'statement of objective'. Whilst suggested methods of achieving those are outlined, often in detail, in the final analysis, you can appeal to the spirit of the regulations. It is up to you to demonstrate that your solution achieves the OBJECTIVES.
In the case of drains, these are a sufficient flow rate to keep them running freely, a provision to prevent build up of noxious and combustible gases, and a provision to prevent these gases from appearing inside the dwelling.
Any combination of slopes and pipe diameters and vents and u-bends and traps and durgo valves that achieves this 'meets the regulations'