u/virgoduh

27/7 - in-person appointment at us embassy London

05/08 - passport mailed by US department of state

11/08 - email from us embassy london asking for postage (next day required)

13/08 - Royal mail notification that passport is otw

14/08 - missed delivery

15/08 (today) - picked up passport from post office

16/08 - flight tomorrow

Cut it really close but everything worked out!!