Okay. So Bristol's Britain First aircraft had flown in 1935, and had proven faster than the RAF's very latest fighter prototype, so the head of OR branch decides to go with a paper airplane and a totally unproven engine instead. That's a bold move.
Nevertheless the OTL RAF did order several paper aeroplanes with totally unproven engines into production. However, (as we both know) the results were mixed.
Prior to 1935-36 Air Ministry policy was to:
- Issue a specification;
- Order prototypes of the most promising designs;
- Evaluate them at the A&AEE or MAEE and based on the results select one or two designs for further development;
- Order a small pre-production batch for service trials, and;
- Finally order the winning design in quantity.
From 1935-36 it adopted a policy of ordering aircraft into production "off the drawing board." That is aircraft were ordered into production before waiting for the prototypes to fly and the results of their evaluation by the A&AEE or MAEE. The intention was that this would get new types into service faster by cutting out two stages of the previous procurement policy. This was a high-risk policy and AFAIK the Cabinet and Air Ministry were very well aware of that. AFAIK is why they usually ordered two types into production instead of one as there was a good chance that one of them would fail, for example the Avro Manchester and Handley Page Halifax.
Another example is the Battle and Blenheim which were ordered into production in the summer of 1935. At that time the Battle was a paper aeroplane with an unproven engine and the Blenheim was a paper plane based on an airliner, albeit with proven engines. The prototypes of these aircraft did not fly until 10th March 1936 and 25th June 1936 respectively. (You have counted Britain First as the Blenheim prototype. I have not.)
The first contract for 155 Battles was placed in the summer of 1935. I don't have the exact date, but going by the contract numbers (424738/35 and 435061/35) and the production specification numbers (23/35 and 28/35) it was before the first 150 Blenheims were ordered (22nd August 1935). The prototype K4303 did not fly until 10th March 1936 and according to Bowyer underwent brief trials at the A&AEE in July 1936. K7558 the first production aircraft made its first flight on 14th April 1937 and the first 155 production aircraft were delivered between May 1937 and May 1938. The Battle entered RAF service with No. 63 Squadron in May 1937.
Under the old system the Air Ministry would have waited until the prototype completed its trials at the A&AEE before placing a pre-production order in August 1936 and the first quantity production contract a year after that.
Britain First (the sole Bristol 142 airliner) made its first flight on 12th April 1935. This became K7557 under Contract number 419009/35 when it was taken over by the RAF and sent to the A&AEE for trials. The Bristol 142M bomber was built to Specification 28/35. The first 150 aircraft (K7033 to K7182) were ordered on 22nd August 1935. The first of these K7033 flew on 25th June 1936. According to Thetford this was the prototype Blenheim bomber and according to Bowyer in Aircraft of the Few it was the closest the Blenheim had to a proper prototype. Bowyer says that its A&AEE trials lasted from November 1936 to February 1937. According to Thetford the first production aircraft was K7034 which left the factory in November 1936 and according to him the Blenheim entered RAF service with No. 114 Squadron in March 1937. My copy of Air Britain's RAF Serials K1000-K9999 says the first 150 Blenheims were delivered from January 1937 to January 1938. Bowyer says that deliveries to the RAF began in March 1937 and that even one year later aircraft were being delivered incomplete. For example no turrets were fitted until nearly 200 hundred Blenheims had been delivered.
The Battle prototype was built to Specification P.27/32 was issued in April 1933 and was ordered on 11th June 1934. Its competitor the Armstrong Whitworth A.W.27 flew on 6th December 1936. According to the British Aircraft Specifications File priority was given to the Whitley bomber which is why the A.W.27 made its first flight so long after the Battle's prototype.
I suggested in Post 190 that De Havilland proposed a twin-Merlin powered aircraft to Specification B.9/32 (which produced the Hampden and Wellington) or P.27/32. In the latter case a single prototype of the twin-Merlin De Havilland aircraft would be ordered in place of the Armstrong-Whitworth aircraft of OTL and like the Battle (and the Spitfire) fly in March 1936. It was a paper aeroplane with an untried engine in the TTL summer of 1935 but so was the Fairey Battle in the OTL summer of 1935 and that didn't stop the Air Ministry ordering 155 of them.