Hi Hugo, No risk I know of, and I'm pleased yours is ok, But it does have a negative effect on local plant and insect life, long term, if not controlled we have had/having serious invasive problems from this plant on a golf course over Cheshire way, even to the point that the club is being sued by surrounding properties, this is after some serious clearing by the ground staff, I was afraid that a similar situation could arise here.
I did not know if it was a local problem, but thought better to check it out.
This plant under control such as yours, is OK but, when the seeds reach open areas, such as the Orme, it could be very damaging.
So still looking for advice........