How we develop projects

We undertake a phased options appraisal and assessment process when developing proposals to reinforce our network.

The options appraisal process has been designed to meet our duties and also follows other relevant policy and guidance when making judgments and decisions on the project. This has included consideration of the relevant National Policy Statements, the Holford Rules (which apply to the routeing and design of overhead lines) and the Horlock Rules (which apply to the location and design of substations).

Further details on these policies and guidance can be found in the Corridor Preliminary Routeing and Substation Siting study (CPRSS).

We are currently at the Options Identification and Selection stage of the process and we are seeking feedback during this consultation on our work to date. Your feedback will help to shape our project as we move forward.

Project development and appraisal process


The Holford and Horlock Rules

National Grid employs two sets of rules and guidelines for the routeing and siting of new energy transmission infrastructure:

  • The Holford Rules: provide guidelines for the routeing of high voltage overhead transmission lines. These are important guidelines during the development of a preferred alignment and considerations of whether certain sections should be undergrounded.
  • The Horlock Rules: provide guidelines for, the design and siting of substations (in addition to cable sealing end compounds and line entries). When considering new electricity infrastructure, National Grid has regard to the degree to which options comply or deviate from these rules.

More information

Options identification and selection process

Find our more about options identification and selection.

Our proposals for public consultation

Learn more about our proposals for public consultation.