Thanks Jörn, I had convinced myself that they were Indian Meal Moths. I'll check my peanut supplies more carefuly in future (and my breakfast cereal!).
Encouraged by Mikes comments (thanks), I've put out my first batch of 'larvae enriched peanuts' today. The first suprise was that there were lots more larvae with the frozen peanuts, which indicates that they carried on eating/growing for quite a while after putting in the freezer. I'd put them in a bag, inside another bag which was fortunate as some of them had escaped the first bag.
I'll watch with interest to see if the birds enjoy them.