As the railway system spread throughout the UK so it took over the carriage of mail from the horse and coach. A very fascinating area to collect along with postcards of the trains the stations and also maps showing the development of the various lines. The key reference book is 'TPO's of Great Britain & Ireland' by Wilson  - out of print but we occasionally handle copies - please let us know if you would like to be informed when one becomes available.  The leading society for collectors of railway cancels is: