The war was certainly advantageous to Guy’s commercially. It cannot be said how the company would have fared had the war not come along but, by the time it ended, the company had a large, well equipped plant, up and running, and an established name.

Immediately after the war there was very little production, partly on account of a world wide recession and partly on account of the vehicle market being flooded with army surplus. But the war had demonstrated the reliability and usefulness of motorised transport, and had produced a large number of people who knew how to drive. This produced a rising market, which Guy’s were able to get into.

When civilian vehicle production re-started in 1919 Guy started to produce lorries and his first charabanc. Those two lines were to be the basis of the company’s future but they also embarked on a number of experiments which were less successful. They produced a road/rail vehicle, an electric vehicle chassis and a gas lorry running on charcoal. In 1919 they produced the Guy car, of which about 200 were produced, production ending in 1922.

In the inter-war years Guy’s developed and produced a range of lorries, buses and, from 1926, trolley buses, all of which incorporated innovative features. 

Sometime in the 1920 Guy’s adopted the "Feathers in our Cap" slogan, with the Red Indian head following somewhat later.

In 1928 Guy’s took over the almost bankrupt Star vehicle company in an exchange of shares, and production of their cars continued for some time thereafter, finally ceasing, for lack of sales, in 1932. 

It seems that Guy’s were not sufficiently profitable to be able to make the investment needed to keep Star going and were, indeed, themselves in financial difficulties. But another world war was came along.

On the basis of a successful war, from 1946 onwards Guy continued to develop and produce new buses, trolley buses and lorries, at one point becoming one of the largest such manufacturers in the country. They also had very large export sales.

 In 1948 they acquired Sunbeam-Karrier, thus enabling Sydney Guy to buy out at least what was left of Sunbeam. Production of Sunbeam trolley buses and Karrier buses continued for a while at the Moorfields site but by 1953 the Karrier name had been dropped and all production moved to Fallings Park. By now the works at Fallings Park covered 14 acres and up to 1,500 people were employed.

During the later 50s the company became financially unsound. It is certainly arguable that their bus and lorry designs (trolley buses having by then been abandoned nationwide) were not on the leading edge and sales seem to have been falling off. Profits were non-existent.

In 1966 Jaguars became part of the ill-starred and ill-remembered British Motor Corporation (later British Leyland), who had plenty of other bus and lorry makers within their group. Production continued at Fallings Park but increasing competition, both nationally and internationally, lead to falling sales. Guy’s started to assemble Scammel tractor units, as a way of using spare capacity, but all production ceased in 1978. 

The decline and fall of Guy’s had contributed greatly to the general economic decline of Wolverhampton in the 1970s and to rising unemployment.