"Where by virtue of an order under this section the liability of a person to maintain a highway is extinguished … [I interpose that it is an application to the magistrates for an order to extinguish liability that has the consequence that the highway becomes maintainable at the public expense - see section 53(1)] … that person is liable to pay to the highway authority for the highway such sum as may be agreed between him and that authority or, in default of agreement, as may be determined by arbitration to represent the value to him of the extinguishment of his liability."