I didn't measure the leaves in situ, but I think that they're too large and with too many final lobes for Saxifraga hypnoides (3-5, rarely more). (The plant in the photograph was maybe 8 inches across.) I'm not familiar with most saxifrages, but I'd expect Saxifraga hypnoides to have a more "mossy" appearance; I thought that this was more like Saxifraga rosacea. Also I understand Saxifraga hypnoides to like lime, and this plant was on Millstone Grit.
In the field I was thinking of Ranunculaceae, on the lines of Aconitum or Nigella, assuming an unfamiliarity with young growth, though when I did come across young growth of Aconitum some years back it was Anemone that I confused it with.