Hi Count
Your moth is a Silver Y Autographa gamma. This is a migratory species which comes in from Europe in large numbers every year. They tend to be mid Summer to Autumn up here, though they can occur outside that period. They certainly bred in the south of the UK but if they do so up here I do not know. Winter survival of the larva in UK is very rare, so the ones we see every year are new immigrants. They can be very hungry on arrival and it is common to see several feeding together during the day on nectar rich plants like echium. The larva feed on a range of plants including nettle - yet another reason for keep an area of that much abused plant in the garden!
Hope that helps
Pterodroma
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