The supplier may propose and sub contract some warranty work to BT or a third party in case of minor interventions or specific agreed work. The supplier shall ensure that proper training and technical knowledge are sufficient to perform quality work in an efficient manner. The supplier will cover any cost (labor, materials, tool/equipment, etc.) and remains responsible for the work.Such sub-contracting of warranty work will be laid down and agreed in a Supplier Warranty Service Agreement subject to the following principles:"