Green Carpet.
(Colostygia pectinataria)

It seemed to like the warmth of my hand and wouldn't go away.

Information:
The pattern of blobs and crosslines on the forewing is distinctive. The colour, however, fades very quickly from this, newly emerged moth's bright green, to a white with, at most, only a hint of green but often with a tinge of pink instead - it can then be very confusing.
Flight times are May-September when they can be seen almost everywhere there is a bit of greenery. They are quite common, resident and very well distributed throughout most of Britain.