L.A.R.P. Civil Defence Instructor lapel badge

[High Wood]

I was wondering if anyone can please tell me the significance of the letter L before the A.R.P. in the title of this badge. Is it anything more significant than 'Local'?

The badge has some interesting provenance as it came with a Defence Medal in its original box named to a Mr M.R. Atkinson of 5, Appleby Close, Ilkeston. Derbyshire. His entry in the 1939 Register gives his occupation as a Certificated Assistant Schoolmaster but, perhaps more interestingly he is also an A.R.P. Warden in Ilkeston.

This badge may be offered for sale along with the paperwork at some point in the future.