Trade tokens were originally issued by traders as low value coinage to fill a gap in currency available to the less well-off. There's an interesting article about 17th century versions on the Museum of London website, but their use was known in the 18th century and later also. 

This is an image of an Allison & Docwra one shilling token used on Billingsgate Market. Allison & Docwra is listed by Neil Todd (trade token collector, author and authority) under Billingsgate. He found no record of the partnership in the directories of the time but he suggests an ephemeral merger of George Allison & Co (1901-08) or G Allison Ltd (1909-24) and Docwra & Co (1906-08). We are still trying to find more information about who actually issued this token and when they date from. Any additional information about it is welcome.

Notes: Billingsgate was the London wholesale fish market.

[Source: DFRP Collection]