CAP 168 is probably based on an ICAO specification but I have no definite knowledge of that.
The ICAO source code is Annex 14 - Licencing of Aerodromes.
CAP 168 follows Annex 14, except where the UK CAA has filed a 'difference'. Usually, the UK CAA attempts to follow ICAO pretty closely.
Actually, it's all a bit circular, 'cos Annex 14 is largely based on earlier work done by the UK Ministry of Aviation, which preceded the CAA.
We provide lighting in accordance with CAP 168. However, many airlines operate to JAR Ops which allows them to operate when certain parts of our kit aren't working. This can vary from company to company. Thus, if there are variations at an individual aerodrome, some operators will be able to land and take-off, others not.
Cheers,
The Odd One