You will not find anything in the AIP regarding unlicensed aerodromes or runways. The requirements for a licensed aerodrome (and therefore runway) are in CAP168 Licensing of Aerodromes. An unlicensed aerodrome does not have to meet these requirements but may well do. The only way to find out is to telephone the particular aerodrome and ask.
CAP428 Safety Standards at Unlicensed Aerodromes may be of interest (available on the CAA website.)