I colleague had exactly the same problem with his wifes mini clubman it turned out to be wheel alignment he had to have ot done on a regular basis, the speed humps near his house apparntly played havoc with the suspension according to the tyre shop which he uses minis are quite prone easily to mis alignment.

Just to be clear:

you replaced two unevenly worn tyres without having any checks carried out to identify the cause?

Get it to somewhere with a four wheel tracking kit pronto or you'll just wear out the new tyres the same way.