The Scottish government approved the plans for the network of 600 pylons from the Highlands to central Scotland.

The project, an upgrade of an existing lower voltage line, attracted 18,000 objections.

Colin Hood of SSE said Scottish ministers had imposed "substantial conditions" on the project.

These will involve an element of putting cables underground at Beauly and also the removal of a power line through the Cairngorms National Park.

Mr Hood, SSE's chief operating officer, said: "While the new line, like its predecessor, will be overhead, these conditions mean there will be a net reduction of over 100km (62 miles) of pylon lines in Highland Scotland as a result of the Beauly-Denny upgrade.

"The conditions will require significant technical, engineering and environmental resources and will cost tens of millions of pounds."

Mr Hood added: "We are aiming to make good progress in satisfying Scottish ministers with regard to them, we have already started consulting with key stakeholders and we are planning to start preliminary construction works this year."