Germany can ramp to Sea Lion at any juncture in the game. There are clear signs when he is about to do it; saves or just got tons of money, stages mass armor and air onto West Germany.
UK doesn’t have a lot of money in this version. It also doesn’t have a proper defensive force. Taranto pulls a lot of your airpower away so it is very vulnerable.
That’s why buying some bulk early is good. Fighters are especially useful because they can threaten ships, land on US carriers to help and extend range, and help with subhunts.
The key here is thinking from the Germany players PoV. If he sees you have 12+ units and 2-3 fighters, he could still potentially build on you and SBR you, but its going to be hard. If you have more, and some ships, he will probably just say forget about trying because Russia is an easier target and even if he could still overwhelm UK, USA will rescue it, and it wont be worth the cost.
On the other hand, if you make it easy for him, remember, hes bringing like 10 ground units + 12 air PER WAVE, so no matter whether we are talking about stuff he has at start or stuff he buys, Germany can ramp up at any moment and its attacks, though costly, are fairly likely to succeed if he goes in 100% and UK didn’t turtle with every dollar UK1-3