BR class 375 on SEHS is actually BR class 377. EDIT: Oh, sorry, It's the refurbished 375. My knowledge about British trains is not very good yet.
Its quite ignorant that some people say its just a repaint of the same thing. For a start, if you compare the cab controls and layout its quite different.
It's like when people accused DTG of repainting the Class 40 into railfreight livery and passed it off as a Class 37, albeit less stupid. EDIT FOR CLAIRTY: I'm not calling the OP (or anyone else for that matter) stupid, I'm saying the argument is.
They are similar, but contrary to popular belief, not identical. They have key differences to other Electrostar types. Southeastern do operate 377s though; they are in First Capital Connect purple with light blue doors and a Southern interior. DTG could probably add them to SEHS as they run to Gillingham.