Hi I think the museum is open summer weekends, is a very interesting place.
I grew up nearby(long after its closure) and it maybe my next book project after Blackbushe.
Basically opened by Phillips&Powis local motorcycle dealers around 1928. Initially as a aeroclub and aircraft dealers. Then appears F.G. Miles looking to establish a a production line for his new Hawk aircraft. During the 30's the airfield and factory slowly expanded until Miles gets the contract for the Magister then the Master from the RAF. By then end of the war around 5000 people employed.
There was also an RAF EFTS based from 1938 until around 1953, there were also a RAF comms flight based. The EFTS flew a succession of Magisters, Tiger Moths, and Chipmunks.
With the end of the war the Monitor and later M52 contracts were cancelled and the Marathon severely delayed by government meddling. So despite good sales of the Gemini,Messenger and Aerovan the company folded in 1947. Handley Page took over the Marathon project and built the early Heralds there. The airfield was pretty quiet after the RAF comms flight left for White Waltham just leaving a few private aircraft. Handley Page moved Herald production to Radlett in 1962 and the airfield closed shortly after. It was almost untouched, if overgrown, until the late 70's when the current housing estate was started. The original factory survives almost intact and is used by industry.