LMH: I spend most of Monday poking, prodding, twisting, stretching and bouncing up and down on the offending foot with varying, but not particularly extreme, levels of discomfort...then doing the same to the other foot. The main conclusion I came to was that if you try to beat up on your feet it can hurt a bit!
Notwithstanding fears of stress fracture (a likely diagnosis if you're a closet hyperchondriac) and gangrene (I suppose if your forum name is Blisters it's reasonable that you would know something about afflictions of the foot), a more prosaic reason would be a change of running shoes or the fact that my orthotics, nine years old, are getting a bit battered.
Depending on the outcome of my doctors visit I think I'll get myself down to a podatrist. Realistically I can't train hard without orthotic support as I have a leg length difference of 15mm (broken femur in a motor cycle accident in the 1960s) and high arches combined with a pronounced forefoot running style.
Poor biomechanics....moi?