I have no idea. There is a picture of the innards on the CEF site but I can't see any lable to say if one is input and other output:Can it be wired with the meter supply in from the top and out to the CU from the bottom? I am assuming yes, but wanted to check before I ordered it.

100A SP+N Metal Switch Fuse
Metal door and robust metal enclosure, 1.0mm thick steel with low smoke and fume epoxy paint finish
www.cef.co.uk
I doubt it is like the Schneider quadbreak switches where both fuse ends are isolated when off so direction unimportant, but hopefully if you pull the fuse cartridge forward it is isolated before you can touch the end!