Overview on the pipe work of the Grand-Orgue. From front to back: Flūte Harmonique 8', Bourdon 16' (with chimnies), Montre 8', Salicional 8', Prestant 4', Bourdon 8' (also with chimnies), Flūte 4', empty place, Doublette 2', Plein-Jeu, Basson 16', Trompette 8' and the Clairon 4'. The highest 5 notes of the reeds 8' and 4' are flue.
Looking close, you can see a keyboard between the feed of the front pipes.
Instruments | Duke's Hall of the RAM, London | Grand-Orgue