Service Bulletin 150A dated August 1954 (Home Trade Circulation Only) is giving instructions about adding 1-1/2" diameter reflectors on the rear of XK120, Mark V, Mark VII and 1936-48 saloon models, pursuant to the Act which required them on all vehicles beginning Oct '54 in the UK. SS100, SS1 and SS2 are not mentioned BTW.
Part numbers are given for reflectors and brackets.
I think I have them on my '38.
They are marked B.S.2515 G2 (heart shaped logo) LIC.2628.
The service bulletin describes prising out some small reflectors from the centers of the setscrews securing the bumper bar.
Mine has no such small reflectors.
Here are the screws I have.
They fit the square holes in the bumper. The reflector brackets fit on them too.
Am I to interpret this then, that the reference to small reflectors in the center of screws, applies to later cars, and not mine?