Mine's now long gone, along with the car, but it was somewhat different. Mine had a squarish, bakelite (I think) face place and (IIRC) a slightly smaller pull knob. I'm pretty sure it was a factory option, though, since I was able to buy a replica face plate many years ago from TRF.
Oh, and probably should mention my car was TS71909L, a later TR3A; there might have been "early" and "late" versions of the ash tray.