War Agency Survey Inspection. Abbreviation was used to indicate that the individual was employed by a war-related agency and subject to a survey or inspection.
Sandra, I can't tell if this is just a guess, or if you have some source to back this up.
I am dubious for three reasons. First, this was September 1939 so while there was a War Office, most other government organisations still had their peacetime title. Technically speaking the country had only been at war for 27 days at that point. I can find no mention of a War Agency in TNA, Hansard* or elsewhere. Secondly "Survey Inspection" is tautologous. since in this context they mean the same thing. And lastly, in 1941 the War Damage Commission was set up to inspect and assess the damage to real property ('hereditaments') caused by enemy action, principally bombing, and to award payments to cover the cost of repair. If there had been a pre-existing Agency such as the one you mention I would have expected this fact to be noted in the
War Damage Act 1941 since no doubt the War Damage Commission would have subsumed some or all of the duties of the earlier agency.
* there is one
reference in Hansard between 1 January 1930 and 31 Dec 1945 to a 'Central Prisoners of War Agency'.