I bought my Vertex watch from Exchange and Mart in the early 70’s, if I remember correctly for abut £5 10shillings and sixpence.
It is one of the dirty dozen watches. I also have a Cyma issue as well. These were the first wristwatches specially commissioned for the British Army during the Second World War. I do like Military or Aeronautical watches. My favourites being Heuer Pilot Automatic and a Marvin Flying Dutchman watch which were issued to KLM Pilots in the 1950’s.