Sat at the console in this picture is Dr John Rowntree, organ advisor to the Diocese of Northampton. With the front panel removed a board is visible which supported the pneumatic action. Each key is connected to the soundboard by a lead pipe, and air pressure in this pipe controls wind being admitted to the pipes which actually make the sound.
However there was also evidence that this replaced an earlier tracker (ie purely mechanical) action. When the pneumatic action was dismantled evidence was found to suggest that it was installed in 1902.
The restored instrument will have an electro-pneumatic action. The change in action and the addition of the reed stop to the organ will mean that we lose the Grade 1 listing, although the sound will not be different. It is possible that the original listing was based on the mistaken belief that the pneumatic action was the original installed by Gern.