According to Norman Peach, if I have read it right, in an article in Classic Bike Guide, February 1999, he says the enamelling shop was moved to Fisher's Green in the winter of 46/47.
"The High Street had engine assembly, cycle assembly, road-test, the canteen, PCV's office and Phil Irving's, the welding shop, the hardening shop, the drawing office and the test house. At Fisher's Green there was the machine shop, enamelling, polishing and initially the Service Department, though together with the spares, this was also moved to the High Street in 1950."