Update:

Had the front of the Millie up on axle stands today, with both wheels off...

Brakes are fine, calipers are tight, no movement from the discs, no warping, pads are still looking almost new.

What we did find though, was that there's a bit of play on the n/s driveshaft. You can grab it and move it about half an inch towards the hub. There is only a minute amount of movement on the o/s, and no movement on Dal's puma. So we're concluding that this is what's causing the noise. Obviously, without actually dismantling everything we can't tell what's causing the movement. As far as we can determine, it's either one of the CV joints on the shaft, or worse case scenario, it's where the diff joins the driveshaft. (The garage that changed the bearing did mention that it could be the diff, but didn't really give any reasons why they thought that.)

So next step I think is biting the bullet and asking a local garage to have a look at it, and keep my fingers crossed that it's not the diff gone tits up!