Bill, Not sure about the time frame, but the name Birmalux comes to mind. I have a plain tubular Birmalux post that was pressed into service on my PX-10 because I was using an Ideale IR90 saddle with flat bar alloy rails that required such a post. I also searched Velobase for British seat posts but found only one example, by Brooks, circa 1930.
John Hurley
Austin, Texas, USA