Just as their attacks on Fighter Command's airfields were threatening to become a decisive advantage for the Germans, they made a tactical mistake which was of such importance that it was arguably the turning point of the battle. With the time available for any invasion of Britain becoming shorter as autumn approached, it was thought by the leaders of the Luftwaffe that the best, and quickest, route to final victory was to attack a target which would compel Fighter Command to commit all its remaining forces to defend. Therefore, on 7 September, the Luftwaffe switched its assault to London.

The Germans felt that the targets attacked so far had suffered sufficient damage and that an onslaught on the political heart of the country would decisively weaken the British will to fight on. As 11 Group was not expecting raids on London, its forces were not in position to defend the capital and the Luftwaffe inflicted heavy damage, particularly in the docks and among the homes of the East End.

7 September had been a victory for the German bombers but, by switching its attack from the vital sector airfields, the Luftwaffe gave the home defences a valuable opportunity to recover. London as a target was further inland than previous objectives. Home squadrons were thus presented with more time to intercept incoming raiders and the endurance of the German single-seat escort fighters in the battle area was reduced.

The decisive day was 15 September when Fighter Command was able to deploy as many as seventeen squadrons to counter a series of large-scale German attacks. After heavy and sustained fighting, during which the Luftwaffe lost 60 aircraft, it became obvious to both sides that German tactics had failed. Fighter Command had not been swept from the skies and invasion was not a viable possibility. Although fighting continued, sometimes heavily, for another few weeks into October, the action on 15 September had proved that the Germans could not win the Battle of Britain.