Aside from being small and dark, not really much to look at aside from it having strongly evident dark discal spots, a hint of a pale spot on the thorax and faint witnesses of pale tornal spots. As it was clearly a male, I decided to have a go at brushing away the scales and checking the abdominal plates. Male pugs have plates on the ventral surface of the 8th sternite, and the shape of some of these is distinctive enough to confirm species (though a lot look very similar on the illustrations I have).
Anyway, it turned out to be a Golden-rod Pug - some 18 years after the last record (but, again, almost certainly not 18 years since the last one in the garden!).
Abdominal plate, showing a quirky and deeply forked kink to the left