Once you have made your search and are viewing all the available cars. Look down the left hand-side menu for a filter " Limited or Unlimited Mileage " and make your selection. Normally the cheaper the rental rate, the more likely it will come with Limited Mileage. For example Green Motion & EasiRent allow 100 miles per day and charge 0.31p per mile over that, per day., This is payable at the desk.