Hi Tony,
Well, they are nothing to do with scotching wheels! They are Rope Shorteners, least, that is what we called them. I used to use these often when testing and calibrating winches on British Army vehicles and plant. We even dug one up once, around the back of the Workshops, it had a wartime date on it, so I restored it and gave it to the REME Museum. That one was made by Trewhella, who made small hand winches. They were part of British recovery kit.
There use is for shortening winch ropes, for instance, you need maximum effort on a winch, which means down to the bottom layer on the drum, but the winch vehicle is close to the casualty and you could have 150 feet of rope or more, so you clamp the rope in this device by rolling it around the part pulley shaped part, then locking the handle down, this wedges the rope, then the pull can be made on the loop end.
Richard