A distinctive element of the Sapphires was the traditional Armstrong Siddeley V-shaped radiator grille with the Sphinx motif mounted on it.

On some models the sphinx sported aircraft wings carrying tiny Armstrong Siddeley Sapphire jet engines.

The six-cylinder 3,435 cc engine had hemi-spherical combustion chambers and could have optional twin Stromberg carburettors(£25 extra)[6] which increased the output from 125 to 150 bhp (93 to 112 kW) giving a top speed in excess of 100 mph (161 km/h).

[6] The body was available as a four- or six-light (two or three windows on each side) at the same cost and with either a bench or individual front seats.

It featured a longer-wheelbase chassis (extended by 21 inches or 535 mm) and a body incorporating a limousine division.

The big-end and main bearings were now made of lead-indium, and a vibration damper was fitted to the nose of the crankshaft.

Servo-assisted 12 in (305 mm) Girling disc brakes were installed on the front wheels, and Burman recirculating ball-power steering was standardised, reducing the turning circle by 4'6".

A Borg-Warner–type DG automatic gearbox was fitted, incorporating a lever on the fascia to hold an intermediate gear at 35, 45, 55, and 65 m.p.h.

The Star Sapphire won the £4,000 four-door coachwork class at the 1958 Earls Court Motor Show ahead of a Princess limousine and a Jaguar Mark IX.

[12] A Star Sapphire saloon with automatic transmission was tested by the British magazine The Motor in 1959.

Prices including tax October 1958 The Mk II version (1960) did not proceed beyond prototype stage; only one was produced.