As is my custom, I can find something to quibble about!
The front of this car shows no sign of the dumbirons that a M45 has and my Frazer Nash guess (above) was based on that lack of dumbirons/semi-elliptic front springs. The later Lagonda V12 had independent front suspension as did the LG6 six-cylinder car and I'd say the front end points to it being i.f.s. - but by then Lagonda had hydraulic brakes which this special has not.