The total number of fighter a/c the RAF had 'on the books' has nothing to do with how many were actually available to actually engage the enemy. The 10 airfields (15 Sqds) in 13 Group for example were too far removed from the action over south-east England to send a/c.
Luftwaffe Order of Battle--August 1940
Establishment Strength Serviceability
Bombers 1,569 1,481 998
Dive-bombers 348 327 261
Single-engine fighters 1,011 934 805
Twin-engine fighters 301 289 224
Reconnaissance 246 195 151
Ground attack 40 39 31
Coastal 94 93 80
Total 3,609 3,358 2,550
Aug 10 1940
Strength Summary
Number Type Strength Svcble
42 1/3 Kampfgruppen 1482 1008
9 Stukagruppen 365 286
1 Schlachtgruppe 39 31
26 Jagdgruppen 976 853
9 Zerstrergruppen 244 189
3 Nachtjagdgruppen 91 59
14 Seefliegerstaffeln 240 125
http://www.geocities.com/CapeCanaver...g40.html#13Aug
The LW had ~2700 a/c (bomber types and fighters) based in France vs how many RAF fighters in south-east England?
In mid Aug, 11 Group had 23 Sqds, 10 Group had 10 Sqds and 12 Group had 15 Sqds. Not all of 10 and 12 Group could be used. So around 600 fighters were available to intercept the LW attacks. The LW had, at a minimum, an advantage of 4:1.