Hi Sgould, is the car an estate.
This happened to me and turned out to be a combination of trailing arm bushes and camber at +3 on both rear wheels, ie folding in. Once I sorted the camber she was fine.
Strangely, she would eat a different corner each time, front or rear.
Park on a level surface, put a small level on the wheel rim, measure the gap to the vertigal, each 1 mm is approximately equal to 1 degree, ( cos theta is approximately equal to 0 for small angles ). I installed 2mm of shims on the top inner hub to bring back to approximately 1 deg.
Hope this helps, I got through 12 tyres in a year trying to get to the bottom of it.