The groat is a fourpence coin. Circulation issue groats (like this one) had the Britannia reverse; Maundy Groats did not.
Head of Queen Victoria facing left, ribbon in hair; around, VICTORIA D: G: BRITANNIAR: REGINA F: D:.
Figure of Britannia, draped and wearing helmet, seated facing right holding trident and resting right hand on an oval shield which bears the crosses of the Union flag; around, FOUR PENCE; in exergue, the date 1851.
The Rotographic catalogue "Collectors’ Coins Great Britain 1760 - 1970" lists mintage of 594,000, probably in error.