Dan_pub has it correctly. Yes, it is the Marshall M.A.4 - and as to that from which it evolved, curiously both dan_pub and fabfour are correct because it was based on the Auster T.7 prototype which, in turn, was a modified Auster AOP.6. So both of you gentlemen can pour yourself a half litre but dan_pub takes the baton!
P.s. does anyone know if there was a Marshall M.A.1, 2 or 3?