Vauxhall Astra both of my rear tyers are bold on the in side

There must be something badly worn on rear susp , possibly bushes or mountings causing steering geometry to be out . Either that or something bent .

Agree with above post unless they have been on the front and swapped to the rear?

not sure steering geometry will cause rear tyres to wear on inside but do you carry a lot of weight in the back of your vehicle?

Mistake to say " steering " geometry . Rear alignment ,settings and geometry , whatever you want to call it need checking after eliminating any wear on bushes or mountings .

No you were right to say steering geometry as something wrong at the back could effect the thrust line ,which will affect steering geometry.