Its uneven wear, with the worst on the inside of the tyre Alex. Hard to see because of the shadow caused by the wheel arch. I think the previous owner swapped the tracking-damaged front ones with the rears, seeing how much better the front ones currently are.
I have been having trouble keeping the pressures correct, the ones given in the handbook look wrong after I've put air in . (It doesn't help having them given in kilopascals..) Pretty sure it's not that though.