Aircraft Landing Code (ALC) – WW2

Can anyone advise on the format of, or have an example, of the Aircraft Landing Code which was introduced for Civil Aviation in the interests of security at the start of WW2?

Quoting from AP 1134 The Second World War 1939-1945; Meteorology:

The Aircraft Landing Code (ALC) is available for use (by civil aircrew), and should be used when operating over the United Kingdom. In the case of the Empire flying boat services in particular the ALC should be used when requesting weather reports from Poole. The ALC has been prepared to provide a secure means of passing meteorological information from the ground to aircraft about to land. Instructions for the preparation and decoding of messages are given in Annex I to these Instructions.

(The ‘Instructions’ refers to the Standing Instructions for Civil Aircraft Operation (SICAO) which were agreed before the war between the Met office and Directorate General of Civil Aviation.)

Brian

PS Before anyone suggests it, I’ve been unable to find any direct reference to this in the Met Office Library & Archives.