1943 London Region Invasion Defence Organisation ID Card

I've come across a few items relating to invasion defence but haven't managed to read a full account of the organisations yet. From what I gather, local authorities created the organisations and members were taked with maintaining local systems in the event of invasion. I believe this included assisting the army in the area (advising on locations of petrol, food, shelter etc) and also to manage refugees passing through the area.

The little I have encountered on the subject seems to relate to the period when the threat of invasion was at it highest - summer 1940 through to summer of 1942. This card is dated 1943 and the organisation was still being maintained.

If you know more about the Invasion Committees and Organisations, please let me know.

1943 Defence Organisation London Region Invasion ID Card