There was a huge clump of this at RHS Harlow Carr but the area was redesigned a few years ago and the plant split up and planted in other areas of the garden. It must be an older variety, possibly planted when Geoffrey Smith was head gardener at the then Northern Horticultural Society garden in Harrogate, Yorkshire.
I've tried for years to find an ID for it.

Looking at my photos from RHS Harlow Carr I think this is Minuteman.

Are you sure it's not good old-fashioned 'Undulata Albomarginata'? Although I allow that 'Minuteman' also has leafy flower scapes.

Whatever it is I want it, so if you do successfully identify it, please do let us all know!