Not to sure what yours looks like but here are a few Octagonal rings;
<acronym title="The Portable Antiquities Scheme">PAS</acronym> record number: NLM-A22FA3
Object type: Finger ring
Broadperiod: Roman
County of discovery: North Lincolnshire
<acronym title="The Portable Antiquities Scheme">PAS</acronym> record number: WILT-BC8C71
Object type: Finger ring
Broadperiod: Roman
County of discovery: Wiltshire
<acronym title="The Portable Antiquities Scheme">PAS</acronym> record number: NARC-EC8B41
Object type: Finger ring
Broadperiod: Modern
County of discovery: Northamptonshire
<acronym title="The Portable Antiquities Scheme">PAS</acronym> record number: IOW-6A52C5
Object type: Finger ring
Broadperiod: Roman
County of discovery: Isle Of Wight
<acronym title="The Portable Antiquities Scheme">PAS</acronym> record number: HAMP-D47894
Object type: Finger ring
Broadperiod: Roman
County of discovery: Hampshire
<acronym title="The Portable Antiquities Scheme">PAS</acronym> record number: LANCUM-F35852
Object type: Finger ring
Broadperiod: Roman
County of discovery: Gloucestershire
And there are a lot more, apart from one modern they are all Roman. The patina should give the game away Val, any chance of popping it up again?
PS. a belated "nice find"