I believe the British Officer is Neil Campbell, who was assigned to accompany Napoleon to Elba: https://books.google.com/books?id=i5oIAwAAQBAJ&pg=PA103&lpg=PA103&dq=neil+campbell+Napoleon+vernet&source=bl&ots=10sy3CibOL&sig=Bl7Irb_YCIrvi3bVIDIhyd0bqOA&hl=en&sa=X&ved=0ahUKEwiQ-N32uZ3RAhWkx4MKHVAnBQ8Q6AEIKjAD#v=onepage&q=neil%20campbell%20Napoleon%20vernet&f=false