Pleased to see something more colourful and patterned than the Common Quakers in the actinic moth trap last night. A quick lookup in the book confirmed it as Nut-tree Tussock (Colocasia coryli). Very distinctive, but fairly common in Southern England.
The species likes Birch, Hawthorn, and Hornbeam, none of which are present in our garden, although there are birches fairly nearby. This specimen is a female? How do I know? 47 eggs laid in the pot by morning. I will leave them to hatch and release them on to a suitable deciduous tree once they do.
According to UKMoths, the species flies April to June and July to September in the south (double brooded); May to June in the north.