Spitfire the History, page 142, Chapter "A temporary expedient" (ie. Mark V)
Letter dated 18 June 1940 (my bad, not april) from Sholto-Dougles, C-in-C of FC is quoted, saying that despite decision taken in November 1940, Spitfires are still delivered with fabric covered ailerons and its only now that production line started to use metal ailerons. Large number of Spitfires need retrofit, but Supermarine is only able to retrofit
at 10 sets of ailerons per week.
Great book btw, suggest order from publisher, dirt cheap. Mordin out.