[5] The original registered office was in Middle Street, Brighton and in 1916, a garage was built in Freshfield Road, which was repeatedly enlarged as Southdown grew.

Companies acquired included Royal Red Coaches of Hove and Eastbourne operators Foard's, Cavendish, Southern Glideway and Chapman & Sons.

This service later known as the South Coast Express, and eventually including Royal Blue into the joint operation, continued until the 1970s.

Southdown's early orders favoured Tilling-Stevens chassis until the outbreak of World War II,[7] although some all-Leyland Titans provided the company with its first closed top vehicles in 1929.

[citation needed] World War II was a difficult time in many ways for the company, although the casualties from enemy action remained low.

Southdown's assistant traffic manager devised a scheme to overcome delays caused by the blackout on country routes by extending journey times on evening services, ensuring that connections would be maintained.

In 1946, a co-ordination agreement with the Portsmouth Corporation was reached with the aim of restoring pre-war express services and coaching excursions, splitting mileage and ticket receipts between the two operators at a 57:43 share, with Southdown being the minority shareholder.

1950 also saw the introduction of scenic open top services from Brighton to Devil's Dyke and Eastbourne to Beachy Head, operated by wartime Guy buses converted to open-top vehicles.

The company also controlled three services operated by Sargents of East Grinstead although these passed to Maidstone & District in 1951.

The post war building programme continued with garages established at Crawley, Hassocks, Moulsecoomb and Seaford, while bus stations were opened in Chichester, Haywards Heath and Lewes.

[12] Southdown did not take deliveries of rear engined double deck vehicles until 1970, when it purchased a batch of ten Daimler Fleetlines with Northern Counties bodywork for delivery to Brighton & Hove,[13] as well as a number of Bristol VRTs with Eastern Coach Works (ECW) bodies painted in green and cream livery.

There was, however, an influx of rear-engined double decker vehicles into the fleet, starting with Bristol VRTs and later Leyland Atlantean AN68s with Park Royal bodywork.

1971 also saw the transfer of most Crawley services to and from London Country - a newly formed organisation within the National Bus Company.

The Stage Coach brand was also applied to occasional services to Winchester and Salisbury (710), Hawkhurst and Canterbury (718), Windsor and St Albans (735), and Oxford (738).

[22] Southdown's existence ended effectively in April 1992 when the company changed its name to South Coast Buses Ltd and split into two divisions.