An interesting statistic I found at the Science Museum in London was that the Spitfire and Hurricane had he same kill rate, but the Hurricane had a higher loss rate. This made me think that if Spitfires had been ordered from Hawker, Gloster and CCF in Canada in place of the Hurricane then Fighter Command would have lost fewer pilots in the Battle of Britain (KIA, WIA and MIA). That would have allowed Dowding to increase the number of pilots per squadron or as fewer replacements were needed the length of the training course in the Operational Training Units could be increased so that the replacement pilots would have been better trained when they got on a squadron.
Malta would have been better off it had been defended by Spitfires to the middle of 1942 instead of Hurricanes. More Spitfires instead of Hurricanes in Greece and Crete would not have stopped the Germans, but the RAF might have inflicted heavier losses on the Luftwaffe. Again I don't see it speeding up the war in North Africa, but Spitfires instead of Hurricanes would reduce RAF losses and increase those of the enemy. Substituting the Buffaloes in the Far East with Spitfires would be nice, but I doubt that there would be enough of them to prevent the loss of Burma, Malaya and Singapore. However, the Japanese would loose more aircraft and aircrew when the bombed Singapore and that might help the Americans at Midway and Guadalcanal. No Sea Hurricanes and more Seafires would be nice, especially if the folding wings version was available earlier.
What the Air Ministry could have decided to do was order 600 Spifires from Hawker in 1936 instead of 600 Hurricanes. Then all other things being equal an extra 475 Spitfires would have been delivered by September 1939, 1,676 by 01.07.40 and 2,546 by 15.10.40. It would also have been better if Gloster had built more Spitfires instead of the Henley. Then an extra 122 would have been "on charge" at the outbreak of war (I don't know the number delivered) and all 200 would have been delivered by 01.07.40.
I also think Westland (which did build Spitfires and Seafires later in the war) should have been ordered to build Spitfires in place of the Lysanders and Whirlwinds it built IOTL. I also think Boulton Paul should have been ordered to build Spitfires instead of the Defiant.
Not building the Lysander was due to a change in army co-operation policy between the ordering of the prototypes and placing the first production contract. That is the RAF and Army decided on a mix of fighter-bombers for CAS and light aircraft in the AOP and LL roles in place of a specialised type like the Lysander.
Assuming that Boulton Paul and Westland were able to build Spitfires at the same rate as the Defiant, Lysander and Whirlwind a total of 568 Spitfires would have been delivered by the outbreak of war instead of 305 Spitfires and 263 Lysanders. They would have equipped 15 squadrons instead of 10 (and 5 Lysander squadrons) IOTL.
1,635 Spitfires would have been delivered to 01.07.40 instead of 909 Spitfires, 108 Defiants and 618 Lysanders. They would equip 31 squadrons at home and overseas, when IOTL there were 19 Spitfire, 2 Defiant and 10 Lysander squadrons.
On 15.10.40 total deliveries had increased to 2,449 (1,426 Spitfires, 267 Defiants and 756 Lysanders IOTL) and there were 35 Spitfire squadrons (19 IOTL plus 3 Defiant and 13 Lysander squadrons).
IIRC The Defence of the United Kingdom, the eponymous official history on that subject said that the Air Ministry considered ordering the Spitfire and Hurricane "off the drawing board" in 1935 instead of after the prototypes proved satisfactory, but instead the first orders for 300 Spitfires and 600 Hurricanes were placed in 1936. If they had been ordered "off the drawing board" in 1935 then the production problems might have been sorted out a year earlier than out timeline.
IOTL an order for 6 Supermarine Stranraer flying boats was cancelled and production of the Walrus flying boat transferred to Saro so that Supermarine could concentrate on building Spitfires. ITTL the initial Spitfire order is for 34 aircraft in August 1935 in place of the original contract for 17 Stranraers placed on the same date. I'm also going to order 8 Seafires with folding wings in place of the 2 Supermarine B.12/36 heavy bomber prototypes. 17 extra London flying boats are built by Saunders Roe instead of the 17 Stranraers and Walrus production is transferred to Saro at year earlier as well.
The Hawker Spitfires ordered in 1935 might be in place of the Fury II or some of the Hart based aircraft ordered from Hawker in that year. It might be possible for Gloster to build more Hurricanes instead of some or all of the 750-odd Gladiators that were built for the RAF, FAA and export. Although it was built to a specification issued 4 years before the ones that produced the Spitfire and Hurricane, it entered service less than a year before the Hurricane.