When the mainline railways obtained air powers from Parliament in 1929, only the Southern Railway responded, albeit with an unsuccessful attempt to gain control of Imperial Airways. When a small number of internal airlines sprang up in different parts of the country in 1932, the railways did take note, the Great Western Railway initiating a service between Cardiff and Plymouth in 1933, but only for the prestige of being the first in the air. This was soon followed by a network of air services between Birmingham, Cardiff, Teignmouth, Torquay and Plymouth. These services carried mail and passengers. The GWR services were soon succeeded by Great Western & Southern Air Lines.

In 1934 the Big Four railways formed Railway Air Services Ltd with Imperial Airways as a nominal shareholder but also providing pilots and engineering. This company, Railway Air Services Ltd, was registered on the 21st March 1934. It was formed by the Big Four railways (LMS, LNER, SR and GWR) in partnership with Imperial Airways. Each railway company and Imperial Airways provided a director and the Chairman was Sir Harold Hartley from the LMS. The purpose of Railway Air Services (RAS) was to provide and operate air services in the British Isles and elsewhere and to form connecting links with the services of Imperial Airways.

The first service in 1934 was sponsored by the SR between Croydon and the Isle of Wight and was followed by a GWR one between Plymouth and Liverpool, but it was the LMS that sponsored most services, its main ones being between London, Birmingham, Manchester, Belfast and Glasgow. Competition was intense, however, especially in the Irish Sea area. The LNER alone did not sponsor services in 1934, nor subsequently. Each railway financed the necessary aircraft. In December 1938 the Great Western & Southern Air Lines subsidiary of Railway Air Services was formed to fly its southern and midland routes.

The objective of the railways was to control the new internal airlines if the persisted in staying the course. One of the weapons of the railways was the booking ban whereby there was a threat to withdraw the franchise of agents who sold tickets for airlines not on the Railway Clearing House approved list. The ban on some airlines was lifted when the agreed to restrict their operations. In several cases, the railways actually withdrew their services in favour of a new airline owned jointly with the competitor.

The behaviour of the railways was to a large degree influenced by the LMS chairman Sir Josiah (Lord) Stamp and the SR general manager Sir Herbert Walker, who both never flew and wasted a lot of time worrying about the airlines. During World War II, when many services were suspended, the railways gradually bought out their partners in the jointly owned airlines. In 1944 the railways published a plan for the development of air transport to Europe. A change of government brought to an end the railway involvement in air transport. The Railways Act 1993 extinguished the 1929 air powers which British Rail had inherited in 1948.