Single line staff and a set of two keys, Wise's patent, 1886. The staff is engraved 'A to B' and 'B to A'.

Single line working is one of the more dangerous aspects of railway operation. Trains often travel in either direction over a single line section and can only pass at passing loops or stations. Signallers control access by issuing a staff or tablet, unique to a specific section of single line, to train drivers as authority to proceed. This ensured only one train was in section at any one time.

Where single lines might experience more than two trains travelling in the same direction in succession, a method of working was developed to ensure the single line staff is not taken to the wrong end of the section. Called ‘staff and ticket’, a train staff unlocks a box containing paper or metal tickets. The signaller issued individual tickets to give successive trains authority to enter the single line section. Both staff and ticket must be shown to the driver or guard before the ticket is accepted. The staff, retained by the signaller, is issued to the driver of the last train entering the section. It is then surrendered to the signaller at the exit, allowing the process to repeat in the opposite direction.

To prevent errors such as the traincrew being inadvertently shown the wrong staff or ticket, Berkeley Wise of the Belfast and Northern Counties Railway patented a train staff that featured lockable metal tickets in 1886. A key to one of the locks was retained by the signaller or station master at either end of a single line section, allowing tickets to be issued for one direction only until the staff was received and the tickets reattached, allowing the process to repeat in the other direction.

Adopted by some Irish and Welsh narrow-gauge lines, light railways and the standard-gauge Buckley Branch of the Wrexham, Mold and Connah’s Quay Railway, Wise’s Patent Train Staff did not see widespread use.