Top bolt on the nearside. I've tried to figure out whether it would have been a different story had it been the other bolt (or the other side) but have drawn a blank so far. It's the style of caliper where the pads sit in a cradle and then the caliper bolts to that with two sliding pins, too - might have been a different story had it been the kind where the pads install directly into the piston/caliper body with a spring clip!
All sorted now, £2 for a bolt from the main stealers. I won't do that again!
Worst thing was I didn't even need to take the caliper off... on the other side I unbolted the entire carrier bracket as one. You live and learn!
@Can'tWeld I hope you cleaned & degreased the threads then used some blue loctite on the bolts, like you should on all brake caliper bolts. That's maybe why it loosened in the first place!