The clues that lead me to Bognor Regis-
The roof supports and valancing had the look of a Southern station
On a fine day seagulls normally stay close to the coast so I first considered all stations close to the South East coast.
The clue I spotted was the reflection in the windows of a overhead lighting support so I then considered all stations which have floodlit carriage sidings adjacent to a coastal station. It left only a few others such as Dover Priory, Ramsgate. In looking at photos of these and other locations the roof supports were different.
......open floor....