Moray, Scotland

Name for this grass/sedge, please? The plant is six feet tall.
It appeared in our garden a few years ago then flowered for the first time last year. It is not the sort of thing that would have seeds used in bird feed nor do any of our neighbours grow it.
One feature that does not appear in the pics is that the sold leaves have minute hard hairs up the edges of each leaf, pointing upwards towards the tip. If I run my fingers up the leaf than I dont feel them; run my fingers down the leaf then they are very obvious.

• 2 Jul, 2019