Scented sweet violets, nestling under a hedge.
I think this is wavy bittercress. It has a zigzag flower stem, 6 stamens (2 shorter than others – I needed a lens to count them). It is not frost hardy and shouldn’t be flowering until March-April, but it has been very mild. Like hairy bittercress, which grows everywhere in our garden in the summer, it is edible with a peppery taste like watercress.