Mileage is currently at 131,925. Not a low number but I guess it's technically "low for the year".
I do have to point the wheel slightly right to stay straight.
So, is uneven tow in possible but not a good idea or simply not possible to achieve? I'm wondering if the tow in on the nearside is wrong and causing it to wear like that.
Am I right in thinking it can't be a camber issue as it's a live axle and the hub is bolted directly to the axle?
The toe in would be controlled by the longer steering link - its tied to the distance between the front wheels, so it can't be only one side (as you'd steer to correct it it would wear both tyres not just one of them as Richard said above).
Balljoints though if you regularly hit rough surfaces (another thing common in MK) can take a pounding - mine were bad enough to fail MOT at 170k (on a Disco but they are the same bits). Though would expect on the outside edge would be down to the top one not being right, which would be unusual as the bottom one is the usual one to fail (top one gets swapped at the same time as you have to remove it to replace the bottom one, so you'd fit a new one at the same time)
I'd be inclined to do what Richard says with the wheel - swap it, and see if your steering issue goes away, if so its the tyre causing it now its worn, then monitor what happens with that wheel as far as the tread wear goes.