On 1 July 1933 the MR, along with London's other underground railways aside from the short
Waterloo & City Railway, was taken into public ownership as part of the newly formed
London Passenger Transport Board (LPTB). Despite being 44 miles (71 km) from London,
 Quainton Road became part of the
London Underground network.
[note 13] By this time, the lines from Quainton Road to Verney Junction and Brill were in severe decline. Competition from the newer lines and from improving road haulage had drawn away much of the Tramway's custom in particular, and Brill trains would often run without a single passenger.
The main building of the second Quainton Road station
Frank Pick, Managing Director of the
Underground Group from 1928 and the Chief Executive of the LPTB, aimed to move the network away from freight services and concentrate on the electrification and improvement of the core routes in London. He saw the lines beyond Aylesbury via Quainton Road to Brill and Verney Junction as having little future as financially viable passenger routes. On 1 June 1935 the LPTB gave the required six months' notice to the O&AT that it intended to terminate operations on the Brill Tramway.