Yes, as others have pointed out, it's a Mathieson!
They were one of the great British tool makers of the Victorian era, together with firms such as Norris and Preston.
They were predominantly a plane maker, though like most firms of that era they made a huge variety of other tools, as you have found! I have seen another Mathieson brace, but it was a different pattern.
These things are old. I can recall my Grandfather talking about Mathieson planes. He bought a lot of tools in the 20's and 30's but even then Mathieson tools were regarded as antiques. Their planes were first class. Unlike post war planes, most of which need a degree of 'fettling' to get hem right, Mathieson planes were correct from new. That costs, of course, and none of these tools were cheap!
I wouldn't like to try and date your brace, but it could be a lot older than you think. Most Mathieson tools I've seen date from the last quarter of the 19th Century, but sometimes you find one a lot older, but not a lot different. I once smoothed the edge of a plank with a Mathieson plane a friend was using. It was in superb condition, and cut beautifully. As far as my friend was concerned it was just a decent plane, and he had no idea how old it was!
I don't know what your plans are for this tool, but personally I would, very carefully, restore it and keep it. Bear in mind, that even when the Titanic was fitted out, this would have been an old tool!
