Ecucoin

Ecucoins were a form of currency used in the United Kingdom in the late 1990s.

The Seventh Doctor paid for drinks at the Gore Crow Hotel with a with a five pound ecucoin made in 1998. (PROSE: Battlefield)

Behind the scenes
In the real world, the (ECU) was unit of account used by the European Economic Community. Despite the prediction in the 1991 novelisation of Battlefield, the ECU was replaced with the euro in 1998. Furthermore, the United Kingdom never adopted the euro.