unusual tyre wear

the outside edge of one of my rear tyres is wearing more so than anywhere else, it is only one tyre defender 90 200Tdi 1991 is it trying to tell me something?

Well for the back to wear like that then it would suggest something like the wheel bearing or damper on that side could cause that or more serious issues like a twisted chassis, dodgy axle.

Was it always on the back, couldn't have been on the front at some point where it has sustained this wear.

it's been on the back for the two years that I have owned it

Have you checked that it's ONLY the outside edge, and that the inside edge isn't as well, which would just mean that it's a bit under-inflated?