Trinovantes Celtic gold 1/4 stater 50BC
'This is an example of the Clacton 1/4 stater - it's not listed in VA, but there's one in the British Museum catalogue, at BMC 192 (where it's incorrectly attributed to the Corieltauvi). These coins were virtually unknown until the 1980s, but we now have records of more than 50 of them, predominantly from Essex, and it seems certain to be the quarter stater type associated with the full Clacton stater. There is strong Gallo-Belgic influence, as you mention - the obverse seems to be copied from the 'three men in a boat' design found on the imported Gallo-Belgic quarter staters, while the reverse is indeed nearly identical to the Clacton stater type. Its date is probably c. 50 BC.
This one will be in the Index as CCI 04.2136'.