A bit of internet searching told me that the first appearance was a practice for a flypast over the Tottenham Hotspur Stadium in north London and the second one was the actual event for an NFL match. The aircraft of course originated from Lakenheath about 60 miles away. 2 F-15C's and 2 E's.
I also noted from the net that a second flypast was to be done this afternoon for the second of two matches. This time I was lying in wait. I was not disappointed - the formation flew right over my house in a holding circle and I was able to grab a quick shot in the few seconds they were visible:

John