In 1958, mileage agreements were reached with the London Transport Executive for services in Crawley and with Brighton, Hove & District Omnibus Company and Brighton Corporation for services in Brighton - establishing Brighton Area Transport Services, similar to the arrangements in Portsmouth established in the previous decade.
It was during the late 1950s and 1960s that Southdown purchased many of the vehicle types most commonly associated with the company, notably the Leyland Titan PD3 'Queen Mary' vehicles.