I've a feeling that we've stumbled across someone who is an expert in the field here lads!
While I bow to your obviously superior knowledge of the historical accuracy - and I make no bones about my knowledge of these things being from old war movies and from reading Biggles as a child ÂÂ

- nevertheless, the fighters would at least in principle be able to engage the enemy, although I'm well aware that the attackers should have "the drop" (literally) on them.
So allowing interceptors to be intercepted via CAP is the simplest, perhaps we can have some better rules...
How about the following for some ideas, both are based around the idea that the bombers and escorts activate at the same time. Option 1 forms bombers and fighters together as a single, large, wing, while Option 2 is more akin to a second layer of CAP. So feel free to shoot my ideas down! ÂÂ
Squadrons of fighters may form up as escorts for bombers (producing a combined formation known as a wing). Declare that they are flying escort before activating the bombers. Neither bomber formation nor fighter squadron may have already taken an action this turn. The whole wing activates on the bomber's initative, but count any blast markers held by the fighters against the bomber's initative in addition their own. Should the bomber fail to activate the whole wing stands down and the fighters may not attempt an action of their own later in the turn.OPTION 1
Assuming the activation roll is successful, deploy the whole wing at the edge of the board as a single, large, formation. The formation can then move (turning as bombers) into position to make a ground attack. The fighters may not contribute to the ground attack (they are watching the skies!). Should the wing be intercepted (either by CAP or later in the turn) the fighters may make a single turn to face any direction after the enemy fighters complete their move (essentially allowing the escorts to turn their weapons on the enemy!). Bombers may not land as part of a wing, and remember that escorting fighters do not receive the +1 to hit when they attack. Escort fighters may only make one free turn even if they are intercepted more than once. The wing disengages as two seperate formations (split any BM acquired as even as possible between the two formations assuming that there is at least one bomber and one fighter left alive, any odd BM can be assigned at the controlling player's choice).OPTION 2
Assuming the activation roll is successful, place the bombers and the fighters at your board edge. Then make the approach move with the bombers as normal, leaving the fighters at the board edge. Should the bombers be intercepted (either by a CAP or later in the turn), the fighters may move to intercept the enemy fighters after they have made their approach move. Resolve any ground flak at this point against all aircraft. The enemy fighter squadron may choose to either continue their attack against the bombers or engage the escorts in a deadly dogfight. If they continue, they must fight their way through the escorts - resolve both the bombers' and the escorting fighters' AA against the enemy interceptors first (the escort fighters do not receive the +1 to hit) before resolving the interceptors who do receive the +1 to hit as normal. If the enemy aircraft choose to engage the escorts, they may immediately turn to face the escorts. The bombers may not fire at all (too much risk of hitting friendly aircraft!), and both side's fire are resolved simultaneously and neither side receives the +1 to hit. Both escort fighters and bombers are treated as seperate formations after activation and accrue Blast Markers independently as normal.Now, these have been written to be tight rules (and possibly are a little convoluted as a result), but essentially you activate the bombers and escorts together and either 1) move them together as a single formation and the escorts can make one turn before the formation fires flak normally or 2) form the escorts as a CAPCAP, moving them in and the enemy can either take their attacks as well as the bombers' defences or turn and fire simultaneously with the escorts. Neither should be as complicated as they look!