The Spitfire did indeed lose control of the skies over the ill fated Deippe raid partly for this reason in 42. However, the situation was reversed in this case as was the situation in the 'Circus' raids over France around this time. The limited range of the Spitfire and the lack of radar would have been factors, as well as the need to adopt a defensive posture. However, throughout the war most aircraft were constantly being upgraded, and the final versions of the Spitfire with a top speed of over 450 mph were different animals than the earlier versions as used in the Battle of Britain (about 350 mph). The combination of factors (as well as the quality of the pilots) make it difficult to make simple comparisons. However the Spitfire is widely regarded as the only aircraft to have entered WW2 in 39, and with the exception of a short period around 42, had the ability to be upgraded so as to remain competitive until the end of the war. I doubt if the ME 262 could have made much impact in an invasion of Britain due to the development issues and lack of range, but this was much later anyway so we could equally speculate that Britain would have been armed to the teeth by this time.
But as Monty and Doppleganger have so eloquently pointed out what of the Royal Navy? I may have mentioned this earlier in this thread but wargames had been subsequently played at Sandhurst (with Adolf Galand being involved) to examine the various scenarios of an invasion of Britain, and in all of them that I am aware of, the Germans manage to make a landing but are stopped well before getting far inland, partly due to logistics but also because the British Army were no pushover. These were not composed of old men and boys as depicted in Dads Army. These were the army which Hitler praised in defensive capability in Northern France during 1940. The retreat to the Dunkirk beaches was a consequence of the collapse of the weaker French corps to the South and supplies being cut off.
