To drop a spanner in the works:
Southend cannot see squawks because they do not have secondary radar, or an SSR feed.
I suppose if you squawk 7600 that will light up a few ATC xmas trees and then somebody might phone up Southend and tell them - IF they suspect you were talking to them to start with...
London Information cannot (officially) see squawks either.
I don't really understand the questions, as the flight appears to be outside CAS. Maybe it is a word play, like many CAA questions?