I suggest Euonymus japonicus (Evergreen Euonymus); recruit from nearby fruiting tree planted deliberately in the nature reserve (garden extension). I can't confirm and E. japonicus is not yet recorded on CNM.
Oups, thanks hawkeye, I overlooked the spines! yes, there are firethorns in the reserve nearby and a huge hedge of firethorns in Rivett Street; so I confirmed firethorn. Will remove.