Pylons are on the march. Britain’s electricity transmission and distribution companies are to announce plans for a £10 billion rewiring of Britain.

A report due this autumn will warn that if Britain is serious about a low-carbon economy then it must string potentially thousands of miles of new high-voltage power cables across the country. The infrastructure is vital, experts say, because most renewable energy will be generated in remote areas such as northern Scotland or the North Sea – whereas most consumers live in southern Britain.

Some fear the new pylons and cables would threaten treasured landscapes, creating dilemmas for environmentalists who would otherwise support renewable energy without question.

“The power-generating industry is about to undergo great structural changes,” said Chris Bennett, future transmission networks manager for National Grid, which runs the high-voltage cable system.

“We are moving from a system dominated by a small number of large power stations to something far more diverse. Our network needs to adapt rapidly to those changes.”

The need for new pylons and overhead cables stems from the government’s planned shift to wind-powered generation.

Britain currently has about 78 gigawatts (GW) of generating capacity, of which about 40% comes from coal, 33% from gas and 15% from nuclear, with the rest from sources such as wind and other renewables.

By 2020, the government has pledged that more than 30GW – roughly a third of the 100GW total capacity needed by then – will come from wind turbines.

About 11GW of this is likely to be sited in northern Scotland and 19GW in offshore wind farms, mostly in the North Sea.

A report due out this autumn by Ofgem, the power regulator, and the Department for Business, Enterprise and Regulatory Reform will say such changes can happen only if existing power lines are upgraded or new ones built to link such areas with the energy-hungry Midlands and southern England.

National Grid has confirmed that it is looking at plans for high-voltage lines across mid-Wales to carry electricity from the many wind farms planned there to population centres.

In Scotland the two main “interconnector” lines that carry power south would not have the capacity to cope with the planned expansion. One option is to upgrade or augment these lines with bigger pylons and more cables.

Bennett fears such proposals could lead to “disastrous” planning delays and is considering an alternative plan to run undersea cables down the east or west coasts of northern Britain, possibly both. The east coast cables would connect to new high-voltage lines at Easington, Co Durham, while the west coast links would come ashore near Liverpool.

Offshore wind farms present separate challenges. Undersea cables carry only a maximum of about 0.5GW, so the 19GW planned for the North Sea would mean at least 40 new high-voltage cables connecting wind farms to the shore.

More pylons and cables would connect the sub-sea cables to the grid after they hit land, with clusters likely around the Wash, the Thames estuary and Liverpool bay.

Britain has about 72,000 pylons carrying high-voltage cables over 14,000 miles. Digging them underground tends to be ruled out as it costs up to £16m a mile, 20 times more than pylons, and it is difficult to disperse the heat generated.

The far greater number of smaller pylons carrying lower voltages has never been comprehensively counted. Most have been in place for decades and few new lines have been built since the 1960s.

In Scotland there is controversy over Scottish and Southern Energy’s plans for a 200-mile line of pylons up to 213ft high to carry “green” power from Beauly outside Inverness to Denny, Stirlingshire. Opponents include Lord Puttnam, the film-maker.

Steve Smith, managing director of networks at Ofgem, said the grid would need investment of about £10 billion by 2020. This is about £3 billion more than the current value of the whole system: “The existing system is incapable of delivering the low carbon power we hope to generate in future. We need to beef up existing lines and build new ones.”

Times recommends

• Energy-saving ideas from switched-on professor
• Rooks are as clever with tools as chimpanzees
• Burping of the lambs blows roast off menu