Here’s how I see it. England has 2 rounds to build before it can attack on England 3 (prior to Germany 4) with their 3rd round being placed after their combat moves.
England starts with: 3 Infantry, 3 Fighters on itself.
England CAN get 2 more fighters and 1 tactical bomber from the Med bringing it to 3 Infantry, 5 fighters, 1 tactical bomber.
Assumptions:
Germany destroyed the British fighter in Normandy on round 1.
Germany sank the destroyer in SZ 109 with 3 fighters, 3 tactical bombers, 2 submarines and a strategic bomber
Germany sank the destroyer in SZ 106 with 2 submarines
Both British transports are sunk, no Canadian units are brought to England for defense/offense.
London is a higher priority than France for Germany. (France might be allowed to fall to Italy, if necessary.)
England starts with 28 IPC, that’s 9 Infantry Save 1 on Round 1.
Round 2: England has 34 IPC (28 + 5 original territories NO + 1 saved) assume +9 Infantry, +1 Armor, save 1.
England has, on round 3:
Infantry: +3 + 9 +9 = 21
Artillery: +1= 0
Armor: +1 = 1
Fighters: +3 +2 = 5
Tactial Bombers: +1 = 1
Strategic Bombers: 0 = 0
AA Guns: +4 = 4
(AA Guns cannot be used to attack, so they are not relevant to a British hit and run on Scotland.)
Germany brought 13 Infantry, 7 Artillery, 5 Armor, and 1 AA Gun to Scotland.
I will use Frood’s calculator. If we change the parameters and state that at least 1 defending unit must be alive at the end of the battle we get:
Attacker: 30%
Defender: 70%
Average units left for the Attacker: 2
Average units left for the Defender: 6
Average number of rounds: 4.6
If we alter it so that at least 7 Attacking Units survive (theoretically that would give England 10 Infantry, 1 Armor, 1 Tactical Bomber, 5 Fighters and 4 AA Guns to defend London with) we get:
Attacker: 100%
Defender: 90%
Average units left for the Attacker: 9
Average units left for the Defender: 11
Average number of rounds: 2.5
Therefore, I really do not see Strafing as an option, Jim. Then again, I believe you originally ran your numbers assuming you could get the 4 ground units from Canada and had the fighter in Normandy. I am assuming those units do not exist (but the Battleships do exist.)