National Grid Pylon Diversion

National Grid is legally required to modify an overhead power line in Colne Valley for HS2 Ltd to allow for the build and operation of the new railway. We’re rerouting and raising the height of a line of electricity pylons on land now in HS2’s possession which the railway will pass under.

To achieve safety clearance five existing pylons carrying a 275kV overhead line across Denham and Hillingdon will be dismantled and the ground around each of them reinstated. Six taller pylons with support foundations will be built in new locations, diverting the line across a lower section of HS2 at a suitable crossing point. The overhead line will be diverted onto these new pylons and connected back up to the existing network.

The work is being done by National Grid and our contractor Babcock. The power line will remain the property of National Grid and we’ll be responsible for its future maintenance.

Our overhead power line diversion work continues until Winter 2021 however the date is subject to change to fit with the activities of other HS2 contractors. National Grid will return to the area later in HS2’s development to construct a Grid Supply Point (GSP) substation connection to power the railway.

This work is on both the east and west sides of the Grand Union Canal; near Skip Lane, Dews Lane, Harvil Road, Denham Country Park and the golf course. During the works there will be shared access along Skip Lane between National Grid and existing users. We’re working closely with HS2 and its stakeholders to maintain access routes for specific user groups while we work. Once complete the new section of overhead line will connect into the existing line at either end.

During the main works in Summer 2021 there will be temporary traffic management and road closures for a short time to install and then remove scaffolding and netting.

Footpaths and bridleways which are already closed for HS2’s main construction works are affected by our diversion. Please visit for footpath alternatives h ere.

Please also view a project leaflet and a map of the route (not to scale) here .

Construction activity is continuing at pace over the Summer when we’ll assemble and erect the new pylon towers and undertake wiring works to connect them up and energise the line. Piling works and foundations to prepare the new pylons are progressing. Some pylons have also been assembled and erected offline in their new positions, waiting for connection of overhead wire.

You may now see more activity and engineers working at height and the use of larger equipment like truck mounted mobile working platforms, cranes, tractors and winches.

Reconductoring of the diversion is done during an electricity outage. This means the power supply is turned off one circuit (one side of the electricity line) at a time to allow work to commence safely. Temporary masts will be erected to divert the electricity supplies temporarily works are being undertaken.

There will be temporary traffic management (lane closures and traffic lights rather than full road closures) as we install and then later remove scaffolding and netting in locations, like across Harvil Road. This is in the interest of safety for users while our works take place. We plan to do most of the netting at night to minimise disruption.

The works at Buckinghamshire Golf Club and Denham Country Park include the installation of a temporary bridge over the River Colne and a temporary haul road with fencing through Buckinghamshire Golf Club and Denham Country Park. This activity is to access the position of one of the new pylons which replaces an existing one in the Park.

Our work is supported by security staff, including HS2 security and where necessary the police, to maintain the highest levels of health and safety of our workers and the public/amenity users. This includes fencing to demarcate working areas and land which is in HS2 possession.

Once the new pylons are ready and the overhead wire is diverted, we’ll dismantle and remove the redundant overhead line and pylons, reinstate work areas and remove the haul road, before handing the land back to HS2.

We’ve produced a frequently asked questions sheet that will cover answers to the most asked questions about this scheme. You can download a copy here .

We understand people have concerns about electric and magnetic fields (EMFs). EMFs are produced wherever electricity is used and there have been suggestions that exposure to these fields might be a cause of ill health. National Grid takes the issue of health very seriously and relies on authoritative and independent scientific organisations such as the World Health Organization (WHO) and Public Health England to review the worldwide body of scientific evidence on EMFs and health, as well as reviewing the science ourselves.

Health considerations are given a high priority in the process by which we arrive at any proposals for new routes for electricity connections. Our approach is to ensure that our assets comply with the guidelines set by Government on advice from Public Health England. A vast amount of research has been done into the possibility of health effects, without establishing any risks below these levels.

If anyone has any further questions or concerned please contact the EMF helpline on 0845 7023270 or EMFHelpline@nationalgrid.com .