Is this species a variant of a red flour beetle?
This does not look like a red flour beetle, but more like some species of Melolontha, possibly a cockchafer. For more specific information, we would need to know, where your back garden is and maybe something to scale the bug. I would go for Melolontha melolontha, the common cockchafer.
Of the two other european species of Melolontha, M. hippocastani usually has a black edge of the elytra (see this picture), which this one doesn't seem to have, and M. pectoralis is very rare and mostly (only?) found in Germany.