I had beetles hatch out in my house in October, attracted to light, I though initially they were furniture beetles but I didn't find enough burrows to correspond with the quantity seen. I have now found ~ 50 dead and alive in a packet of Gardman Swan & Duck Food. The pellets of food now have holes where the beetles have emerged, the pellets contain, 'poultry meat, meat and bone meal, wheat, wheetfeed, soya, maize, fish meal and soya oil'. The beetles look similar to the images of the Rust-red Flour Beetles featuring on the website but the thorax doesn't seem quite right. Is there any other species they could be?
I don't know if you're on facebook Nigel but Graham Finch can help you: https://www.facebook.com/groups/453937838305988/permalink/573926926307078/
He suggests these are Stegobium panacium (which I found recently too) and would like to get some specimens from you if possible?