Certainly this building is very old, and has been hacked about to fit it's use any nuber of times, BUT it had to be for heavy engineering originally as each overhead crane is certified up to 10 tonnes. The cranes were immobilized by Windmill Pine by hanging extractor ducting off them for saw tables etc...
Right next door is Morrisons, Tritton Road branch, which carries a plaque commemorating Wm. Foster & Co factory site on their wall...
BUT take a look at this shot I found on Google, of Whippet production. This is definately the same building. OR Fosters had several which were all exactly the same. However, Rustons across the road only has one equally large building in existence too.