Victoria Clare wrote:
My garden is surrounded by traditional cornish hedges, and being very
sloping, is also crossed by low stone wall/hedges. If I find something
nice when I am trimming them, I sometimes propagate it, and I've also
collected seed from friends' gardens.


That seems fair enough.

I don't think that collecting some seed from free-fruiting plants in other
hedges would do any real harm, given the vast wastage rate of wild
distributed flower seeds, but I haven't actually done that myself (yet).

I completely agree about the seeds. If you can germinate them, then go
for it!