In last night's Courier there was notice of a Planning Application for Withens: "Conversion of former Water Treatment Works to dwelling". Full details can be acccessed via Calderdale's Planning database - use this shortcut:
Withins Clough 06/02012/CON
There's volumes of material to trawl through. You can comment (for/against) online, but N.B. the Works is not actually in the SSSI. Don't be put off by the fact that the Application is made by Keyland Developments Ltd. This is Yorkshire Water in all but name.