This is Saxifraga “Gregor Mendel” x apiculata.
It has been in my little Alpine House all winter although it is a variety which grows well in the garden on a scree slope or in a stone trough.
In case you are wondering an Alpine House is like a greenhouse but it has more opening windows which allow a stronger flow of air. The windows stay open in the winter except when there is a severe frost. The idea is to emulate the weather conditions high up on the alpine slopes which are the source of many of the plants grown.