The service originated in 1891 when the FR Co. was party to an agreement on the carriage of Railway Letters made between the G.P.O. and most of the British Railway Companies (operating through the Railway Clearing House). The agreement specifies firstly the conditions under which the service is permitted to operate and secondly the provision of a label (supplied by each participating railway company) to be affixed to the face of the letter. Railway Letters must bear the full G.P.O. Royal Mail First Class Letter Postage as well as the Railway Letter Fee.