Alongside their work for the British armed forces Vickers-Armstrongs produced military equipment for foreign buyers. Their earliest commercial tank designs failed to sell but in 1928 they produced a masterpiece. Known as the ‘six-tonner’ it was a remarkable design, with a rear-mounted, air-cooled engine driving to a gearbox and track sprockets at the front of the tank. There were two main variants; some tanks were supplied with two machine-gun turrets (Type A) while others carried a larger single turret (Type B).
Following trials the British Army turned it down but the tank was a major export success. It sold all around the world, from South America to Japan and was even studied by the United States Army. It was licensed by the Soviets as the T-26. It was also the direct predecessor of the Polish 7TP tank and influenced tank design in many other countries.
The Bovington Tank Museum exhibit, a (Type B), is displayed in the fancy camouflage style adopted by Vickers for their commercial offerings; it is seen at a mythical army equipment exhibition some time in the thirties.
You can imagine in A Very British Civil War scenario, the Vickers factory making these tanks available to one of the armies for fighting the civil war.