White Ermine.
(Spilosoma lubricipeda)

All white with black spots, legs and antennae - It really showed up in the egg box in the moth trap ... unmistakable!

Information:
They can be mistaken for some colour varieties of Buff Ermine, Water Ermine or Muslin Moth, but the absolute clincher would be to see at least one central black spot on the hindwing. They fly May-July in most town and country habitats, including (wet or dry) grass, gardens and hedgerows. They are very common over the whole of Britain.