So, it seems like a pure sprinter's bike with stiffer tubing. Probably from a location where there was a hard track. Does Herne Hill, Fallowfield or Cardiff mean anything?
From what I can see looks early 1960's. Pure conjecture.
Imported frames are prefixed W so if it is a Danish frame it would be made in Denmark.
RX does not designate one of the well known brands so will be a small manufacturer. Been scouring the web out of pure interest for pictures of track racing in the late 50s/early 60s with no luck.