This coin should come after RIC VII London 25, which is the same except that coin ends with AVG while this one ends with AG...see RIC 28, a SOLI coin with same obverse legend. Not listed in Cloke & Toone either.
Constantine I
A.D. 314
IMP CONSTANTINVS AG; laureate and cuirassed bust right.
MARTI CONSERVATORI; Mars helmeted, in military dress, stdg. r. looking l., holding reversed spear, hand resting on shield; across fields S-F.
in ex. MLL
cf. RIC VII London 25
ex Dr. John Whitehead Collection