Genghis . . .. . seem to remember reading in SIGH FOR A MERLIN that Alex Henshaw was livid almost daily in the 1939-1941 period at the lack of drive and commitment he saw from some of the 'workforce' in aircraft factories, such as at the big works near Southampton.
Different story at Hatfield and Salisbury Hall, as you imply.
212 Mossies were built at Bankstown in Sydney, or at least assembled there, as much of the manufacture was farmed out to companies such as the Beale Piano Factory in Camperdown and General Motors in Pagewood.
On this You Tube clip there is some spirited demo flying by the late Brian ('Blackjack') Walker, one of the test pilots. (If you go to Tocumwal, down on the Murray, where Walker was based for a short period, they will tell you at the museum that he flew a Mossie through one of the huge hangars , built by the Americans.)
https://www.youtube.com/watch?v=c7cVvYdLeek