Update: the little buggers were indeed meal moths:
Things quieted down a little after we cleared out the cupboard, but the buggers didn't go away. I then found an old bag of plain self-raising flour in the back of the (not cleared) top shelf of said cupboard, with one of the buggers in it. A couple of days later, I was going to roast some pine nuts for a salad, and found the pine nuts moved... Larvae
So I threw out the pine nuts, and opened a new bag (which I stuck in a sealed container afterwards), yet the critters still remained, despite me swatting about five of them every evening. Yesterday, I found out the source of the infection had moved to a different cupboard. Larvae in a bag of pasta we ate from just this week
and in a bag of bird food lying in there. So I threw those out, and today, for the first time in 3 weeks I haven't seen a moth yet...
Surprisingly, they never seemed very interested in the freshly opened bags of flour that are still in the cupboard they first originated from, but instead opted for an old bag of self raising flour, pine nuts, pasta and bird food instead.
I'm sure they're hiding, hatching a plan to attack a food source I hadn't thought of...