I have learned how to make it myself:
1/2 cup milk in microwave for 60 seconds until steamy
add 2 tsp vanilla syrup (or 1 tsp vanilla + some sweetener)--more or less
steep a cup of Earl Gray Tea for 3 minutes
Reheat in microwave if your London Fog does not look steamy/foggy enough.
(do they even drink this in Britain?)
Begin day perfectly.