The coins belong to the 3rd century CE from a horde dating to the reign of the rebel emperor Mausaeus Carausius, who, upon learning of orders for his execution sent by Emperor Maximian, formed and defended a small break-away empire consisting of Britain and parts of Gaul. This development led to his being the first emperor to strike coins in Britain for Mr. Crisp to dig up. Ironically, perhaps, Carausius was assassinated by his finance minister.
As it meets the particular criteria, the find is to be officially declared treasure under British law. The link is here.