This is an original tail lamp assembly for the rear of the car.  Red in color. Flat glass. This part is No Longer Available Reference RD7066D 1945-1955 Silver Wraith, Mk-6, R-type, Silver Dawn...

This is the lower Red Rear Stop Tail Light  Lens. 1966-1995 MPW & Continental Models  

This is an original Lucas rear red lamp indicator. This is for the 2 piece tail lamp assembly.  1966-1970 Silver Shadow & T Saloon / Shadow & T Coachbuilt

This is the Lower Red Tail Lamp Lens.   These fit the tail light that has the 2 piece lens with a reflector underneath. If you have the Earlier tail lamp single piece lens with a reflector...

This is the red tail light lens. It fits the tail light with the single lens with a reflector underneath.  L553  If you need the amber lens see part# CD2863