Households could face higher electricity bills unless Britain dramatically accelerates a £70 billion programme to upgrade the power grid, the National Audit Office has warned.
The public spending watchdog said delays to new electricity transmission infrastructure risk leaving the network unable to move growing quantities of renewable power around the country efficiently.
That could force the system operator to spend billions of pounds managing congestion on the grid, with those costs ultimately feeding through to consumers.
Grid congestion costs could reach £7.8bn a year
The NAO said the cost of managing constraints on the electricity network was £1.9 billion in 2025-26 and could rise to as much as £7.8 billion a year by 2030 if required grid infrastructure is not delivered quickly enough.
Constraint costs arise when there is more electricity available in one part of the country than the transmission network can carry to areas where it is needed.
In those circumstances, the National Energy System Operator may have to pay generators in congested areas to reduce output while paying other generators elsewhere to increase production.
The problem has become particularly important as Britain builds more renewable generation, including wind farms in Scotland and other areas distant from major centres of electricity demand.
Watchdog says delivery will be 'very challenging'
The NAO warned that delivering the scale of grid expansion required by the end of the decade would be very challenging.
The programme requires a dramatic increase in investment in the electricity transmission network, with annual expenditure expected to rise from around £2.5 billion in 2025-26 to more than £11 billion by 2027-28.
The wider investment programme is expected to total around £70 billion.
Several projects required to increase transmission capacity are already at risk of being completed later than originally planned, potentially leaving the network struggling to accommodate new electricity generation.
NAO warns of impact on bills and growth
National Audit Office head Gareth Davies warned that failure to deliver the required infrastructure on time could have consequences beyond the energy system itself.
The watchdog said delays could increase costs for consumers and hamper economic growth if businesses and new developments cannot obtain the electricity connections they need.
The NAO also called for greater transparency from the Department for Energy Security and Net Zero, Ofgem and the National Energy System Operator over the progress, cost and risks associated with the programme.
Government says historic underinvestment is being tackled
The Government says it is already reforming the planning and grid-connection systems in an attempt to accelerate construction.
Energy minister Michael Shanks said the findings demonstrated the consequences of historic underinvestment in Britain's electricity network.
Ministers argue that expanding the grid is essential to reduce Britain's dependence on volatile fossil-fuel markets, connect new renewable generation and ultimately bring down energy costs.
The Government's Clean Power 2030 Action Plan has previously acknowledged the scale of the risk, warning that annual constraint costs could rise to around £8 billion in the late 2020s if delays to network construction persist.
£70bn investment programme
Ofgem expects approximately £71 billion of investment in Britain's electricity transmission networks between 2026 and 2031 under its RIIO-ET3 price control.
The investment is intended to provide the infrastructure required for growing electricity demand and the rapid expansion of renewable generation.
However, building new transmission lines, substations and associated infrastructure has historically taken many years because of planning, consenting, procurement and construction requirements.
The Government has introduced reforms intended to shorten those timescales and change the way projects are prioritised for connection to the network.
Clean power ambitions depend on grid
The warning highlights one of the central challenges facing the Government's energy strategy: generating more renewable electricity is of limited benefit if the transmission network cannot move that power efficiently to homes and businesses.
Ministers have argued that moving towards clean domestic electricity generation will eventually protect consumers from volatile international gas prices and help reduce bills.
The NAO's findings show that the financial benefits will also depend heavily on whether the physical electricity network can be expanded quickly enough.
If infrastructure continues to fall behind, consumers could end up paying both for new grid investment and for the growing cost of managing congestion on a network that cannot yet carry all of the electricity being produced.