Steed's Cars - Alvis Speed
Alvis Speed 25 Open Tourer
as seen in Traitor in Zebra.

It is Steed's only vintage car in series 2 of The Avengers, he drives the car only in one episode.

License Plate is CPT 75

CP-series would be a Halifax number ?

Alvis speed 25 Tourer; more photos on the site of Powerful cars
photo above by: www.history-of-cars.com
Unfortunately the colour of Steed's car is unknown, but there were several different tones of the Alvis.

- British Racing Green combined with beige leather seats
- British Racing Green combined with trim colour red
- Dark Blue body colour with grey trim colour

There also existed two tone cars:

Two tone red over maroon (trim colour?)
Two tone cream over maroon (trim colour?)

I would exclude the version British Racing Green combined with trim colour red for Steed's car in Traitor in Zebra, because his car's leather seats look light (in black and white) compared to red seats on photos changed to black and white.