Confidence: I'm as sure as I can be.
Notes: Red-purple blooms in whorls beneath heart-shaped leaves in opposite pairs which are longer and more tapering than Hedge Woundwort esp the lower ones. generally a stockier, more robust-looking plant than Stacys sylvatica (which was growing alongside these specimens). height up 2 about 80 cm
i understand the origin of these plants - at this site at least - has been debated, with some claiming they may not be native but an old introduction or escape.