The finder of this coin asked to remain anonymous. It is a cast potin unit of the Remi, a tribe based in Champagne and Reims is named after them.
The imagery on both sides is rather confusing and difficult to interpret. However, this unit is featured in Ancient British Coins (under coins of Belgica) as the Pigtailed Dancer type (number 82 on page 31). On the obverse is a figure with a pigtail (hence the name of the type) advancing to the right. On the reverse is a creature that has been described as a bear. Coins of this type are not included in the Standard Catalogue.
In ABC this type of potin unit is said to be extremely rare. This specimen is in VF condition but has an edge chip, which reduces both its eye appeal and possible commercial value. My price range would have been a good deal higher without the chip but with it my range would be no higher than £80 – £100.