Dactylorhiza are actually all but invasive once you have one. I suspect that the ones here started from an SRGC seed distribution pack (which were sown, produced nothing, thrown out and then noticed a year or so later....).
About 4 years back there was one nursery at the Chatsworth RHS show/sale event that had them in numerous of their sales plants - I recognised them as large seed/spore-lings and was told that their nusery had them everywhere.
Some of the slip roads on and off busy A roads around here were smothered in them until a couple of years ago - one in particular had a population of very deep-purple-flowered plants. The maintenance of the areas seems not to have changed but I have looked while driving past recently and nothing is obvious again this year, but maybe it is a few weeks early to be certain as yet. Hopefully they will reappear in 2022 - almost no-one will notice, but they are/were spectacular.
