Could have been built by any one of a multitude of builders in the 50's. They all had access to the same basic parts and often built frames to customers specifications so different builders often produced remarkably similar frames. The CO2 pumps were out of fashion by the early 60's but I was still using Nervex lugs as late as 1981 when specified by customers. Looks to be a quality, well brazed frame, some builders were more competent than others.
Freddie Grubb, Maclean, Uppadine, Whitaker and Mapplebeck....... all possibilities but the list is long.
Needs stove enameling and lug lining, it's not beyond redemption. Some nice Chater Lea and Airlight parts would be period correct