WOW .... treat this seriously as the Disco back wheels should always be running dead in line because they are on a beam axle.
Just about the only way for this to happen is a wheel bearing failure, and badly.
It might possibly be a tyre fault, but I doubt it, or a loose wheel .....
Just keep in mind that the real wheels should always be running dead parallel (no toe-in or toe-out) and dead vertical (no + or - camber).
Get a good bubble-level and check if the wheel stands perfectly vertical. Check both sides - if they are good, any error on one will be the same on the other - because the ground isn't level and the landy is leaning a tad.
Check this out as soon as possible I suggest.
CharlesY