On Jan 1st 1935
"1, Not one monoplane bomber was yet in Service with Royal AIr Force.
2. Among the heavy bombers in service, none was of a design less than five years old, and most were twelve
3, The one and only medium day bomber Squadron was part-equipped with a 'new' aircraft,the Overstrand, that was fundamentally some
eight years old
4. None of the light bomber and general purpose squadrons was flying aircraft whose design was less than six years old. "
Above from Mason
Granted there had been a world wide depression which had tended to limit military spending in many countries but the above are the facts as to where Britain stood at that particular point in time. It is not a reflection on what Britain had done in the past or what they would do in the Future. There were only 15 regular RAF bomber squadrons based in the UK with another 13 bomber squadrons in the Auxiliary Air Force. One of which flew the HP Hinaidi mentioned above.
top speed 127mph.
of course this was an improvement over the planes that equipped 5 of the eight heavy bomber squadrons on that date.
The Vickers Virginia X
top speed 108mph.
Things did get better, slowly.
The Fairey Hendon monoplane went into service in Nov 1936 with No 38 squadron
The first Blenheim was delivered to a service squadron (no 114) March 10th 1937
beating the first Vickers Wellesley by a month.
March of 1937 had seen the delivery of the first Whitleys to No 10 Squadron, the 3rd Whitley squadron was equipped in Oct of 1937.
These Whitleys had the Tiger engine
May of 1937 saw the first Battles delivered to No 63 squadron.
Sept of 1938 saw No 49 Squadron get the first Hampdens
Wellington Is were first delivered to No 99 squadron in Oct 1938 replacing Heyford biplanes.
The British did evolve a very powerful bombing force, it just took time and some relearning of the lessons of WW I, as to worthwhile bomb loads and the need for large bombs.