R-reg 406 estate 2.1 tdi

I have a problem with excessive rear tyre wear, wear on both tyres is the
same. (3000 miles from new the inside 2 inches of tread across the tyre is
down to the cords showing while the outside looks new.
Tracking (toe-in style) checked and figures look sensible.
Inner and outer lower wishbone bushes replaced (replaced because the rear
wheels camber angle looked like a triumph herald with far too much weight in
the back)
Car drives OK as it always has done; no clunks.

Anyone any ideas please - or do I take it to a dealer?