More information, this from 'BRITAIN 1939 – 1945: THE ECONOMIC COST OF STRATEGIC BOMBING' by John Fahey
"At its peak in June/July of 1943, the Air Ministry and MAP had approximately 3,619,500 civilian workers under their direct or indirect control182. This figure represents 20.7 percent of the total civil work force available at the time; or over one in every five people." p. 175.
There is a whole chapter on BC manpower. I'll get back to you shortly
