As noted previously Helleborus foetidus self-seeds freely in the borders at the music school and throughout the grounds. I imagine they have increased from a few planted back in the day. Then again they may have already been present in the woodland fringes when the original house was built.

 H. foetidus is a native and grows wild in the UK. It is also a popular garden plant cultivated by the horticultural trade. So sightings of Stinking Hellebore may be wild or a garden escape or even a cross pollination of both!