OK well an answer of sorts (and yes Dale most of it lol) as said it's a Polden hills type but a derivative (which is the experts way of saying they don't know lol) having designs similar to, not Colchester as I first thought, a Later Dolphin brooch and so is dated pretty late for a Polden hills at around 170 AD, there are 3 other known examples though there could be far more that are worn and have lost the comma design from the head, interestingly the other 3 have been found in Worcestershire, Cirencester and Thornbury and so could be unique to the Cotswold villa culture and could explain its late date as the intricacy of the pin/spring would have made it far more expensive to manufacture than the hinged pin it also seems to totally rely on the surface relief for decoration at a time that brooches were increasing being enamelled
That's excellent Geoff, I knew you would get there even if it took all night
Thornbury is surprising all thought there's a lot of Roman activity in and around the area........ Im sure this brooch was found near Gloucester if I remember right, it ties in
Il also pass the info on to the finder the weekend.
Thanks for your help