The 1847 sixpence (Davies 1040) is one of the rarest British sixpences. No examples are recorded as being struck and there are no examples in the Royal Mint collection (p9, Coin Monthly, Jul 1973). Davies mentions 1848-dated sixpences with the last 8 over a 7 (p64, Davies, British Silver Coins Since 1816, 1982), as does Rayner (p160, Rayner, English Silver Coinage Since 1649, 1992) suggesting that 1847-dated dies were prepared.
A single well-worn and graffitied example was brought to light in 1973: the Royal Mint inspected it and found it to be of the correct fineness and that the date did not appear to be modified but declined to confirm it as genuine as they had no records of any being struck or any examples to compare it against (p9, Coin Monthly, Jul 1973). The British Museum could also find nothing to suggest it was not genuine but also declined to confirm it as genuine (p160, Rayner, English Silver Coinage Since 1649, 1992). In 1982 Davies still listed in as unconfirmed (p64, Davies, British Silver Coins Since 1816, 1982).
The single known example sold in Dix Noonan Webb's auction on 29th September 2010 as Lot 1773 for £850 against a £300-£400 estimate.
Also available at Online Coin Club