Hmmm - that's going to be touch and go I think. You'll probably be recovered by then, but the training in the meantime will be your problem - basically a stress fracture will only heal with rest and you're looking at most of the 10 weeks until FLM until you're comfortable, especially if it's your tibia which is the load-bearing one.
So - yes, you probably will be able to run in London, but not as well as if you didn't have it and could train fully.
My advice - book another marathon for may/june, take all pressure off yourself, enjoy London and use it as a long training run. Then go for the later one more seriously.
Best of luck Amanda