Pound sterling

The Pound Sterling — or, less formally, the pound, or quid (DW: Rose) — was a form of currency used in the United Kingdom through at least the early 21st century.

A pound was also a unit of weight measurement.

Unit of currency
Until 1971, the pound was subdivided using a system of 20 shillings to a pound, and 12 pennies to a shilling. (DW: Remembrance of the Daleks)

Susan Foreman caught the attention of her teachers because of her inability to remember how many shillings were in a pound when she and the First Doctor settled down in 1963 London. She erroneously believed that Great Britain had switched to the decimalised Pound, something that would not occur until until 1971. (DW: An Unearthly Child)

Around the late 20th century or early 21st century Britain introduced a five pound coin. (DW: Battlefield).

The Third Doctor and Sarah Jane once discovered that they were in a Parallel universe because £5 notes had a picture of Edward IX. (PHS: Who's Who?)

According to one account the UK was no longer using this currency by 2050, having switched to credits (K9TV: Oroborus) According to another, however, the UK had converted to the Euro sometime before 2062. (NSA: The Last Dodo)

Known exchange rates

 * By 2008, £1 was equal to slightly more than 50 Sto credits. (DW: Voyage of the Damned)
 * £1 was equal to approximately 5.1 Hyspero Dirnas. (OBIW: The Panda Book of Horror)

Unit of measurement
Pounds were a type of weight measurement. The unit was in wide use in at least the United States of America well into the 21st century. Jack Harkness for instance, once gave Massachusetts-born Janet Rae Tanner's weight in pounds in 2011, suggesting that this was the weight measurement in most common use in America. (TW: The Middle Men)