Merlin didnt save Britain in WW2,it was German's decision to postpone the invasion in order to allocate more resources for the USSR invasion..Had they put pressure another week or so, RAF would throw the towel ,luckily Germans were not aware of this !
At no point were the RAF a week away from defeat. On the morning of the 7 September, hours before the Luftwaffe switched the bulk of their attack to London, the heads of Fighter Command held a meeting to discuss their strategy to hold out for the next few months. There was no talk of imminent collapse.
It was the Luftwaffe who faced defeat, although they didn't know it. The Luftwaffe began their main campaign on 13 August. Serviceable, operational aircraft on that date:
Jagdgeschwader (single engined fighters) - 853
Zerstörergeschwader (twin engined fighters) - 189
Kampfgeschwader (bombers) - 1,008
Sturzkampfgeschwader (dive bombers) - 286
RAF Spitfires and Hurricanes - 579
Blenheims, Gladiators and Defiants - 99
On 7 September the Luftwaffe switched to attacks on London. Strength on that date:
Jagdgeschwader (single engined fighters) - 658
Zerstörergeschwader (twin engined fighters) - 112
Kampfgeschwader (bombers) - 798
Sturzkampfgeschwader (dive bombers) - 133
RAF Spitfires and Hurricanes - 621
Blenheims, Gladiators and Defiants - 73
As you can see, in the 4 weeks the Luftwaffe concentrated attacks on the RAF, Luftwaffe strength fell, RAF strength increased slightly.
At no point were the Luftwaffe "winning". The Luftwaffe were incapable of carrying on the battle in the way they fought in August and early September, which is one of the main reasons they switched to attacks on London.