The declared tonnages under the terms of the Washington Treaty for the British carriers were (data from Jordan's "Warships after Washington". NB tonnages vary by a few hundred tons according to source but the following provides a reasonable guide):-
Argus - 14,450
Hermes - 10,850
Eagle - 22,600
Furious - 22,450
Courageous - 22,500
Glorious - 22,500.
Total - 115,350
Treaty limit - 135,000
Balance available - 19,650.
In July 1920 the Admiralty decided to convert Furious and either C OR G to a full carrier. Work on stripping Furious to main deck level occurred before the start of the Washington Conference. Work to rebuild her began in June 1922, after the Conference ended, and so the RN also considered her an "experimental" ship alongside the first 3 listed (but there were some reservations as to whether that in fact held true, see Friedman. Subsequent events meant this was never put to the test).
The Admiralty went to Washington considering its future carrier needs to be based around 5 x 25,000 ton ships and came away with a 27,000 ton limit on individual ships. So 5x27,000 gets the Washington allowance of 135,000 tons.
Later in 1922 the Admiralty, influenced by the outcome of the Conference, decided to convert BOTH C&G. The design wasn't finalised until April 1924 and work on them began immediately but did not complete until 1928 and 1930 respectively.
The discussion makes it sound as though the RN then did nothing until the early 1930s.
Post Washington, the RN worked on plans for new carrier designs based around ships of 10,000 tons (27 knots), 16,500 tons (34.5 knots) and 25,000 tons (34.5 knots). In Nov 1923 the Admiralty endorsed a plan to replace Argus, Hermes & Eagle and use the excess allowance with 4 ships each of 16,500 tons with a speed of 34.5 knots and carrying 32 aircraft. By Oct 1924 increasing aircraft size drove the ship size to 20,300 tons. The first of these was included in the 1926 Programme, then deferred to 1929 then, with the financial crisis, to the 1931 Programme. The late 1920s were also a period when there were hopes for additional disarmament. For the RN carriers, this potentially meant a reduction in the allowable tonnage available. So with a need for 5 carriers, the RN stood a chance of being caught out if it started building new ships too early.
Given the developments in aircraft, arrester gear (new transverse gear first tested on C in Jan 1931 with a full fit from late 1932), crash barriers (first fit in Ark Royal in 1939) and catapult technology (first fitted to C in 1933/34) in the late 1920s / early 1930s the earlier design clearly required to be revisited by the early 1930s.
1931-34 was also a period of change in RN naval aviation. Rear Admiral Reginald Henderson was appointed the very first Rear-Admiral Aircraft Carriers in Sept 1931, a post he held until Sept 1933. He was to prove tremendously influential in RN carrier design through the 1930s. Under his guidance the RN saw the benefits of using larger numbers of aircraft. He used multiple carriers to achieve this during exercises in the Med. This desire for more aircraft is reflected in carrier design in this period.
So 1931-34 sees a lot of work carried out in carrier design, trading ship tonnage and dimensions with speed, armament and aircraft capacity (60+ were envisaged at a time when Courageous was rated at 52). The outcome was Ark Royal ordered as part of the 1934 Programme, laid down in Sept 1935 and then commissioned in Dec 1938. But her sketch design was not signed off by the Admiralty until 21 June 1934. That left a lot of detailed design work to be done through the remainder of 1934, before the normal peacetime tendering process could begin in early 1935.
Rules for replacement were dictated by Treaty and in particular the 1930 London Treaty. Basically the latest an old ship could be retained was 6 months after its replacement entered service, by which time it had to be rendered incapable of warlike service. The RN was not keen on disposing of any of its carriers before it had to. But the 1936 London Treaty removed the carrier tonnage cap (although it reduced the limit on individual ships being constructed) allowing retention of the older vessels.
It took about 3-4 years to build a carrier in the 1930s (the USN was the same). Start too early and you lose out on the benefits of advancing technology requiring refits and their associated costs later. Maybe some tonnage can be saved from the 1920s design by reducing the speed requirement. But it is only a 32 aircraft ship.
Ark Royal was a radically different ship from that contemplated in the late 1920s. Larger, slower with greater aircraft capacity. Could her development have been speeded up? Or would starting to build a new carrier earlier have produced a less capable ship?
As for repeat ships, the problem is again one of timing. Having taken so long to design and order Ark Royal, you then come into the period of the run up to the Second London Naval Conference (held 9 Dec 1935-25 March 1936). There is much prior negotiation going on. Even as early as autumn 1934 the US position was expressed as seeking more disarmament. That even influenced the Ark Royal design because the British position was to seek a 22,000 ton limit for each new carrier and Ark was built to that. The Conference eventually agreed 23,000 tons. Do you order another ship in 1935 so close to the Conference when you don't know what the rules will be when she completes? Perhaps you have a better idea of the direction of travel. Perhaps not. How different would Ark have been with another 1,000 tons in her design?
Late 1935 sees a number of changes. The Director of Plans reassessed the required number of carriers increasing it from 5 fleet to 8 fleet (48 aircraft) plus 5 trade protection and a single training carrier. Couple that with the Oct 1935 Italian invasion of Ethiopia. At that point the design and procurement process is changed and accelerated. The first Armoured carrier designs are called for in Jan 1936 and the final design for the Illustrious class was approved in Dec that year.
The long term plan for the RN produced in 1936 but never formally adopted, although it was adhered to in most respects up to the outbreak of war, called for 1 fleet carrier per year 1936-42 plus 1 trade protection carrier per year 1936-40. Add in Ark and you get the modern front line carrier fleet envisaged by the Dof P, allowing all the old ships to be scrapped.
The historical carrier programme was:-
1934 Programme - Ark Royal (laid down Sept 1935)
1936 Programme - Illustrious & Victorious (designed 1936, ordered and laid down 1937)
1937 Programme - Formidable & Indomitable (repeat Illustrious class and laid down 1937. Indomitable redesigned during 1938 when armour delays become clear, to incorporate as much of the Implacable design as possible)
1938 Programme - Implacable (design begun in early 1938 as a modified Illustrious class, ordered Oct 1938, & laid down Feb 1939)
1939 Programme - Indefatigable (repeat Implacable. ordered June 1939 and laid down Nov)
1940 Supplementary Programme - 1 repeat Implacable planned (Irresistible. Finally ordered 1942. Eventually built as Ark Royal IV)
No trade protection ships were ordered.