The message
from "Ade" contains these words:

I think you're supposed to cut off the leaves of helleborus orientalis in
the autumn/winter,

Only ones which are dead, broken or discoloured, and not till the
plants start flowering in late winter/spring.


but now that flowering is over do I cut off the leaves
(which are big and healthy)

No


or let them grow until next autumn?

Leave them on the plant till next spring; they will protect the crown
over winter. Then, only take off dead or damaged ones.

Janet