This is a very low-growing perennial with almost circular, short-stalked leaves attached to creeping stems which root as they creep over the ground. As the plant matures the foliage becomes orangey-brown. It arrived accidently from its native New Zealand with other plant material and was first noted in 1908. Found mainly on paths and in crevices in walls, it likes alpine conditions, so is widespread in mountainous areas of Northern Ireland and the rest of the British Isles. In fact it is thought to be the only alien plant to have colonised such places.
Weedkillers to use:-
Dichlobenil prevents emergence of seedlings among established woody plants, for up to one year.
Glyphosate, systemic action killing the whole plant, but does not deal with the seeds. A combination weedkiller for use on paths would be best.
See also Broad-leaved Willowherb, Marsh Willowherb and Short-fruited Willowherb with similar flowers, but the growth habit and foliage are closer to Thyme-leaved Speedwell, Blinks or Scarlet Pimpernel.