Thanks for the suggestions. I've so far gone with the further investigation into the problems in the lumbar area and went to see a personal trainer/anatomist who is known locally to be pretty switched on with posture-related issues. She's helped me to see that my pelvis is rotated and upwardly tilted to the right and my lumbar spine is "locked solid" quote unquote - that's the very simplified version as there's a host of other things going on too, obviously.

I've been recommended a physio/osteopath who may be able to help with the jammed up lumbar spine, to be followed by some specific core work, a look at glute firing which is reduced on my left, stretching the ITB, quads and deep hip flexors and internal rotators, and a detailed look at my gait when running, which is currently right side driven. I'll also be doing some strengthening of the intrinsic muscles of my foot, along with the ant & post tibs. All of this before doing any running again.

It's been suggested that barefoot running may load the lumbar spine more than conventional heel strike running, due to with heel strike the shock being absorbed by all three foot arches, whereas with barefoot, due to the ball of the foot landing, the shock is possibly only absorbed by 1 or 2 arches(?) I'll be keeping an eye on this when I get back to running.

So thanks for the advice to date on core and foot related issues, if anyone's interested I'll let you know how it goes, it's going to make an interesting case study if nothing else