An amendment to the Construction and Use Regulations in 1956 saw the maximum length for double-deckers increased to , allowing a wider entrance to be located ahead of the front axle. This was initially to allow the driver to supervise boarding whilst the conductor collected fares, but quickly it became apparent that the design would allow for one man operation. Leyland took advantage of the new regulation to launch the first prototype Atlantean at the 1956 Commercial Motor Show at Earls Court Exhibition Centre. Though it featured the front entrance design that would redefine the bus industry, several factors prevented the bus going on the market. The main problem was the high level of engine noise inside the lower saloon, as the engine was still inside the body, with the compartment being used for bench seating.