How to propogate this?
Can this be divided or is leaving it to self seed an option?
I don't think division is possible but cuttings should work. They self seed all over the place.
edited June 2020
Looks like one of the hypericums to me. Not sure which. Most hypericums self seed happily. You could also try semi-ripe cuttings in the next few weeks.
It’s also probably worth pegging a few stems down, ‘wounding’ the underside and waiting until next spring by which time if may well have layered and you can separate the little plants and move them to their own spots.
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.