WW1 Port of London Authority Railway On War Service Badge

A rare original First World War 1914-1918 period badge, gilt brass circular example bearing blue enamel 'PORT OF LONDON AUTHORITY' title surround, Crown over 'ON WAR SERVICE' to the centre on white enamel ground; the reverse impressed with maker's details 'J.A.Wylie & Co London' and impressed with official low issue number '321'. Very good condition, complete with original buttonhole fitting, enamel intact, gilt finish remains bright. Diameter 28mm.