For the protection of the utility undertakers referred to in this part of this Schedule (save for National Grid which is protected by Part 3 of this Schedule, Western Power Distribution (South Wales) plc which is protected by Part 4 of this Schedule, Dŵr Cymru Cyfyngedig which is protected by Part 5 of this Schedule, Abergelli Solar Limited which is protected by Part 6 of this Schedule, and Wales and West Utilities Limited which is protected by Part 7 of this Schedule), the following provisions have effect, unless otherwise agreed in writing between the undertaker and the utility undertakers concerned.