HVAL has described the issue beautifully.
I have often wondered, when the war starts, how long our aircraft supply will last. Even with excellent performance on the part of crews, it should not take too long for a larger enemy to destroy 100 - 150 Typhoons, be they on the ground or in the air. I do not believe we are in a position to escalate production in the same way as fighter production in WW2, especially given the complexity of the aircraft today. Therefore, the argument about quantity over quality is certainly a strong one, unless the aircraft chosen is the modern equivalent of the Boulton-Paul Defiant or the Fairey Battle.
The UK, IMHO, is busting itself to afford two capabilities that are to my mind unnecessary. Namely aircraft carriers and the JSF. I believe acquisition of these will actually set our defence back decades because they are either the wrong answer to the right question, or vice versa.
Preparation for the defence of the UK should concentrate on adequate numbers of capable assets, be that Typhoon, Mirage or even a Saab, local maritime patrol and protection by the RAF and the RN and research/development of excellent defensive technology such as advanced radar, missiles, UAVs, cyber-type weaponry etc.