The only way Germany would consider an invasion of the UK would be if they had already somehow had a smashing victory over the RN, reducing the fleet disparity to at least 50/50. This is... not impossible, but would require luck for the Germans and intense bungling for the British.
I'm not sure how much bungling. Consider:
France gets smashed. Italy jumps in shortly before the end to get some morsels at the table. Med is now a CP lake, but the RN can't simply let that go...they have to send some reinforcement. Italy and A-H have a good 6 dreadnoughts, with Goeben hanging around as well. That's not an insignificant amount of ships, and doing nothing is not a possibility.
That said, invasion is still not happening. My point is more that it isn't hard to force the RN to make some very hard decisions.