Bloody bike, I've now got a "Look, I'm coming, I'm braking" warning when I try to slow down... courtesy of the squealy front brake. Tried a few times braking from 60 to 20 to see if it was just a bit of corrosion that needed some persuasion to come out but that didn't work either...
Calipers off, plenty of meat left on the pads (but appear to be no-name, certainly don't look anything like the EBC brake pads I fitted to my last bike and my dads bike and are definitely totally organic). Was a very small very shiny piece of (possibly metal) dug into one side of the one pad. The discs are within spec (1/5th of life remaining at 4.6mm/5mm), and there aren't any grooves or severe pitting.
Reassembled everything after scuffing up the pads a bit and brushing off the crap, and giving the discs a good clean... sounds good at walking pace, out again Thursday so shall see if it's fixed! If it's not, I'll get a decent set of EBC pads and give everything the once over. Slight bit of corrosion to the pistons and pins but nothing horrendous.