Since July 1933, Frank Barnwell, Bristol's chief designer, had been working on a small twin-engine low-wing monoplane design, initially intended to be powered by the sleeve-valve Bristol Aquila radial engine, designated as the "Type 135". Rothermere became aware of Bristol's proposal and, in response to his inquiry, on 3 March 1934, Barnwell issued him with a quote of the specification and performance statistics of the design, including an estimated top speed of at . By this point, proposed use of the Aquila engine had been shelved in favour of the supercharger-equipped, poppet-valve Bristol Mercury engine. Deeming it suitable for the issued challenge, the design of Type 135 was further adapted to produce the "Type 142" in order to meet the requirements outlined by Rothermere. In late March 1934, Rothermere placed an order for a single "Type 142" aircraft, under which he paid for half of the estimated £18,500 cost up front and the remainder upon the aircraft's first flight in the following year.