Network charges are forecast to rise from £207 to £342 a year by 2030

Households could face higher electricity bills for decades as the forecast cost of major grid projects rises by as much as 467 per cent.

The upgrades are needed to support Labour's clean power plans, but industry figures have warned that spiralling budgets risk turning the programme into the "next HS2".

An Ofgem review of eight SSE projects in Scotland found that their expected costs had increased by an average of 283.5 per cent.

One senior industry source described the problem as "endemic" and compared it with HS2, which exceeded its original budget by more than 200 per cent.

The source said: "There's a very high risk here, frankly, that grid projects are set to become the next HS2."

If Ofgem approves the additional spending, households and businesses could ultimately face tens of billions of pounds in extra costs through the network charges included in electricity bills.

These charges pay for the infrastructure used to transport electricity around Britain and are expected to become the main cause of rising power bills over the coming years.

Annual network costs could climb from £207 to £342 by 2030, according to figures from the Electricitybills.uk tracker. They would then account for almost a third of a projected average electricity bill of £1,045 a year.

A global shortage of specialist equipment has been blamed for delays and higher costs across the upgrade programme.

Ed Hezlet, an energy specialist at the Onward think tank, described the forecasts as "deeply concerning" and questioned whether the wider pipeline of planned projects could withstand similar pressures.

He said: "Supply chains are difficult right now, but cost increases of this magnitude deserve much more attention from the regulator and the Government."

Mr Hezlet warned that the consequences could last for decades if similar increases affect projects elsewhere in Britain

"If this inflation spreads into other planned transmission projects, consumers will be paying higher electricity bills for decades," he added.

The eight developments in Scotland represent only a small part of the national grid upgrade required to connect more renewable power to homes and businesses.

Ministers have indicated that around £80billion of investment will be needed to support Labour's clean power ambitions by 2030, with total spending potentially reaching £240billion by the middle of the century.

However, the higher forecasts have not yet been approved for recovery from customers.

Ofgem has allowed SSE to increase spending during the early construction stages, but it will carry out a full assessment before deciding how much can be recovered through consumer bills.

The regulator's published framework confirms that costs judged inefficient will not be approved.

An Ofgem spokesperson said: "Ofgem has tough price controls to limit the level of capital spend passed on to consumers.

"These figures have not yet been through the final efficiency assessment. Every penny will be rigorously challenged by Ofgem.

"Nothing is judged efficient just because a network company forecasts it."