The British landline service used a different approach than the American to extend the distance over which a landline signal could be sent. They used a double current system, doubling the voltage difference between the make and break. Some detail of this system can be seen in the diagram.

The key required for this is quite specialized. It is literally two paralleled keys, the polarity of both must be switched between transmit and receive. While it makes for a more complex key, it reduces the number of relays by half since the distance a signal can travel is doubled.

Here you see a close up diagram of the key itself. These keys were first made around 1880. Brass finished keys were used at home, while nickel finished keys were used in the Colonies.

I traded keys with famous British super Collector, G0RDO. This example of the extraordinary double current or GPO key, came from Singapore. It is of the nickel finish type, and was likely made around 1910. The pump handle is horn. The wood case appears to be mahoganey. it is a beautiful work of art, and I am very grateful to John for the trade. be sure to visit his spectacular website of WWW dot MORSEMAD dot COM. If you hear me on the air using a straight key, you can know I am pounding this substantial work of art from the other side of the globe!