JM wrote:
[...]
I don't know why the experts on the gardening programmes enthuse so much
over Acanthus - it's spiny, and invasive, and not easy to get rid of. Mind
you, I can appreciate it for its structure - but only in the large garden of
some stately home!
[...]

From my experience I think it won't be at all invasive if you don't
coddle it. At my last house I had, for topographical reasons, to build
a long raised bed with railway sleepers along the lower side of the
house. I was skint, so I had to fill the bed with some awful stony
subsoil mixed with builder's rubbish. Acanthus loved it: given a start
with some better stuff, they grew well and the clumps increased nicely,
but gave no sign of invasive suckering. Plenty of seedlings popped up
in the path below.

--
Mike.