Little Brick Roadside Hut

When we were up in the Cynon Valley, we came across this really well built brick hut on the side of the road. As you can see, it has it own chimney as well. I have tried to find out what it is and when it was built, so far without success. I can only assume it was built as a winter shelter for workmen who had maybe been caught in one of those dreadful snowstorms which used to be so common in this area. Any ideas folks?