WW1 Rhymney Railway or LB&SCR 1st Issue war service badge

A rare First World War 1914-1918 period "Rhymney Railway" or "London Brighton & South Coast Railway Service" gilt and enamel badge first issue plain border example, the reverse with maker's details "J,A Wylie & Co London" and impressed with official low issue number "Z" "1046". Very good condition, retaining original buttonhole fitting, no damage to the enamel, minor service wear.
Diameter 28mm.

David J. Foggatt book mentions only three Railway Companies whose first issue had a plain edge, "London Brighton & South Coast Railway", "Rhymney Railway" and "Taff Vale Railway", however he says the latter had "TVR" stamped on the reverse. This badge came with two Brecon & Merthyr Tydfil Junction Railway large and small buttons in nickel so I am guessing that it is possibly "Rhymney Railway" unless told otherwise.