Hey Big_Bend,
I think you’re exaggerating the size of the problem. If Germany builds 7 transports on G2, fills them and sends them to Scotland on G3, and fills them again to send them to England on G4, that’s roughly 40 land units that Germany isn’t sending against Russia. Germany is extremely unlikely to ever take Leningrad or Kiev, and so even if Germany drops 20 units in Europe on G5, that means Russia has 4 turns to build up a massive army on the eastern front and then successfully invade Finland, Poland, and Rumania on R4 and R5. The income swing for Russia on the eastern front is almost as big as the income lost by Britain.
When Germany takes London, the factory degrades down to a minor factory, and there is no factory at all in Scotland, so Germany can only recruit 3 units per turn in the UK. That means that if you start building an Atlantic fleet on US2 when you see the 7 transport build, then you can be in position to wipe out the German navy on US4, and retake London with American troops by US6 or so. You’ll need to build enough American boats in the Pacific to stop Japan from winning there, but if Japan isn’t declaring war until J3 or J4, that’s not so hard.
In short, do some damage control. Bring the Canadian infantry over to London to reinforce, if you have a boat that can reach. Build 10 infantry in London on UK2. Fly your fighters back toward London if you still own Gibraltar or Morocco – if your fighters go south on UK1, they should be able to reach Gibraltar/Morocco on UK2 and London on UK3, in time to defend against Germany’s G4 attack on London. Above all, don’t panic. Stop automatically surrendering on turn 4. It’s OK to lose London if you make Germany pay a reasonably high price for it.
If you do something truly reckless like build a minor factory in Egypt and two boats off South Africa on UK1, and then also send your fighters south for Taranto, and you get unlucky in your naval battles on G1, then, I suppose, you could wind up in a place where Germany can conquer London on the cheap and there’s nothing you can do about it.
So, stop using reckless builds on UK1. Build at least 2 inf, 1 ftr in London on UK1 every game – that leaves you enough for a factory or a transport or a couple of subs elsewhere on the board, and it gives you some cushion if you need to switch gears and defend against Sea Lion.