Elstree-St John's Wood tunnel upgrade to boost NW London power
New cables will be installed in the 20-year-old tunnel to increase electricity capacity for homes and businesses.
Trust 40Craft 60Hype 20How this was reported ▾
The central claim is attributed to National Grid, but no named individuals or specific documents are cited.
How well corroborated and evidenced the reporting is. Higher is better.
The article explains the project's purpose and next steps, but lacks direct quotes from affected parties.
Context, balance and separation of fact from comment. Higher is better.
The language is measured, focusing on the technical upgrade and its implications for electricity supply.
How far presentation runs ahead of substance. Lower is better.
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National Grid is undertaking an upgrade of the Elstree, St John’s Wood cable tunnel to increase electricity capacity across North West London. The project aims to provide more power for homes, businesses, and new developments, including data centres requiring significant electricity.
Tunnel infrastructure and logistics
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The upgrade involves installing approximately 60km of new 400kV cable circuit within the tunnel, which stretches from Elstree in Hertfordshire to St John’s Wood in London. Engineers are evaluating the use of the tunnel's existing monorail system to transport materials and personnel during the construction period. A spokesperson for National Grid confirmed that the suitability of existing infrastructure is still being assessed as part of the design process, and the exact methods for cable installation will be determined later.
The Elstree, St John’s Wood tunnel, constructed in the early 2000s, was designed with sufficient space to accommodate an additional cable circuit for future capacity needs. It currently houses the longest alternating current (AC) transmission cables in England and Wales.
Wider programme and new substations
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This tunnel work is a component of National Grid's broader North West London Upgrade programme. This larger initiative includes improvements to over 200km of existing overhead lines between Sundon and Elstree, as well as upgrades to substations at Sundon, Elstree, and St John’s Wood. Additionally, a new 132kV gas-insulated switchgear substation is being constructed at Letchmore Heath to serve five new data centres, collectively demanding around 1GW of electricity.
National Grid states that the overall programme will enhance the resilience of electricity supplies and provide additional capacity for the region. The company also anticipates that increasing network capacity will help reduce electricity constraint costs.
Several contractors have been appointed for the programme. Hochtief-Murphy Joint Venture (HMJV) is responsible for the tunnel upgrades and cable installation, while Laing O’Rourke will manage substation works. Hyundai Electric and Siemens Energy will supply and install key electrical equipment.
Questions this report answers
+What is the purpose of the Elstree, St John’s Wood tunnel upgrade?
The upgrade aims to increase the amount of electricity that can be carried into North West London. This will provide greater capacity for homes, businesses, and new developments, including data centres, and improve the resilience of the electricity supply.
+How much new cable will be installed in the tunnel?
Approximately 60km of new 400kV cable circuit will be installed within the Elstree, St John’s Wood tunnel as part of the upgrade project.
+Will the tunnel's monorail be used during the upgrade?
Engineers are considering using the existing monorail within the tunnel to transport people, equipment, and materials. A final decision on its use is pending further assessment of the infrastructure's condition and suitability.
+What other works are included in the North West London Upgrade programme?
The programme involves upgrading over 200km of overhead lines, improving substations at Sundon, Elstree, and St John’s Wood, and building a new substation at Letchmore Heath to connect new data centres.
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