In 1921, the company exhibited its first articulated vehicle, capable of carrying 7.5 tons, at the Olympia Motor Show. With the demand for this vehicle, the company first moved to a new works in Watford, and then formed Scammell Lorries Ltd in July 1922.
In 1934, Scammell produced the 'Mechanical Horse', designed by Oliver North to replace horses in rail, postal and other delivery applications. This featured automatic carriage coupling and the single front wheel could be steered through 360 degrees. It was sold in 3 and 6 ton versions. The 3-tonner was powered by a 1,125 cc side-valve petrol engine and the 6-tonner by a 2,043 cc engine. Karrier had introduced a similar vehicle, the 'Cob', four years earlier.
From 1937, a Citroën Traction Avant powered version was made under licence in France, by Chenard-Walcker-FAR, known as the 'Pony Mécanique'. This continued in production, in various versions, until 1970.
In the late 1940s, the 'Mechanical Horse' was superseded by the 'Scarab', with similar features but now with a 2,090 cc side-valve petrol engine in both models and a diesel version with a Perkins engine.
In 1967, the 'Scarab' was replaced by the 'Townsman', which had a fibre-glass cab.
The company mainly concentrated on articulated and rigid eight-wheeler lorries, from the 1920s. One vehicle not in those lines that became well-known was the six-wheeled Pioneer. This was an off-highway heavy haulage tractor first produced in 1927. It showed outstanding cross-country performance due to the design that included a sideways rocking front axle, and 2 ft of vertical movement for each of the rear wheels.
The Pioneer was popular in the oil field and forestry (logging) markets, and formed the basis of the British Army's World War II 30-ton tank transporter. With the outbreak of war, development of new vehicles stopped and production concentrated on military Pioneers for use as artillery tractors, recovery and transporter vehicles.
Post war, foreign competition and rationalisation of the UK manufacturers led to Scammell coming under Leyland Motors Ltd in 1955. It continued production in specialist and military markets until 1988 when the site at Watford was closed and the last vehicles under the Scammell name were sold.
Alvis Unipower set up an operation in Watford in 1988 developing trucks and offering ongoing support and spare parts for Scammell vehicles.
The Crusader was a popular vehicle within the UK military as a 6×6 wrecker. Many have also seen use in the heavy haulage industry due to their incredibly strong chassis.