Talking about Brighton station in the 1980s (and probably in the 1970s too), as you exited the station from the concourse through the centre of the building, the ticket office - predominantly for immediate travel - was on the left hand side, and the BR travel centre was on the right hand side IIRC. At some later point (later 1990s or 2000s maybe) the railway operated travel centre closed but became operated by, I think, B&H buses perhaps jointly with some tourist / visitor related role too.
I am not sure what is in either of those locations now, but am aware the ticket office is now off to one side of the station.
You have reminded me that there was, post privatisation, a Thameslink rover type ticket that could be bought from certain tourist related offices so presumably also this outlet on Old Steine