Poster promoting the London-Paris route via Newhaven-Dieppe by the Chemins de Fer de l'Etat et de Brighton. The artwork was by René Péan (1875-1955).
The reference to the Chemin de Fer de Brighton must be to the London, Brighton and South Coast Railway so that dates it as pre-grouping (1923). The style looks Edwardian, almost Victorian, but if the artist and his dates are right it must be post-1900. The Gare St Lazare-Dieppe route was under the Compagnie des Chemins de Fer de l'Ouest, which disappeared on its merger with Chemin de Fer de l'Etat in 1909, so I would place the poster between 1909 and the Great War (1914). Update I was spot on on the date. I've seen a poster in an auction catalogue which gives the date as 1911.
I had the good fortune to return from a continental trip via Dieppe-Newhaven the morning after Liverpool's 1981 European Cup victory over Real Madrid, which was played at the Parc des Princes. I'm not sure whether the highlight of the trip was seeing the working girls plying their trade outside Gare St Lazare at 6:00 am in the morning, or the crew of the ferry at Dieppe turning the hoses on the impatient scousers that tried to climb onto the ship from the quayside cranes. Oh how we laughed!
Keywords: Poster; Chemins de Fer de l'Etat et de Brighton; London, Brighton & South Coast Railway; LB&SCR; Newhaven; Dieppe; Paris; Gare St Lazare; London; Londres; Tower Bridge; River Thames; René Péan; Rouen; 1911; Edwardian; affiche