11. Where in consequence of the proposed construction of any of the authorised development, the undertaker and National Grid require the removal of apparatus under paragraph 4(2) (removal of apparatus) or National Grid makes requirements for the protection or alteration of apparatus under paragraph 6 (retained apparatus), the undertaker must use its reasonable endeavours to co-ordinate the execution of the works in the interests of safety and the efficient and economic execution of the authorised development and taking into account the need to ensure the safe and efficient operation of National Grid’s undertaking and National Grid must use its reasonable endeavours to co-operate with the undertaker for that purpose.