Its impact on the Highland landscape was compared to taking a razor blade to a Rembrandt, but 90 per cent of the controversial Beauly/Denny power line has now been completed.

It has taken over 20,000 tonnes of steel; more than four million nuts and bolts - a million more than the number of rivets on the Eiffel Tower; enough concrete to fill 27 Olympic swimming pools; and transmission cable that would run from Perth to Rome.

All to erect Scottish Hydro Electric (SHE) Transmission’s 124 mile northern section of the line.

Now it’s down to Scottish Power to complete the final 12.5 miles from the Wharry Burn near Bridge of Allan, to Denny.

SHE, a subsidiary of SSE, says Tummel Bridge to Braco, near Dunblane was its last section. The overall project, 600 steel pylons up to 215-feet high replacing an older line, is still on target to be fully “energised” in November. Then it will be able to take extra green power generated in the Highlands and Islands to markets in the south.

However doubt has been cast on whether it will be required to operate at full capacity with subsidies for onshore wind projects due to end next year.

But developers say has it already contributed more than £100m to the Scottish economy and supported the full time equivalent of 1,500 jobs, including direct employment within local communities.

David Gardner, SHE's Director of Transmission, said: “. Its completion is one of the most important steps in securing the future of Scotland’s electricity network and meeting national renewable energy targets.

“The replacement line was designed and tested by our principal contractor Balfour Beatty to stand up to the challenging Scottish elements. And it has already ‘passed the test’ having been battered by hurricane force winds along with snow and ice during the past two winters with no structural issues.

“The project has included the construction of two new substations at Braco and Tummel Bridge and the redevelopment of existing substations at Beauly, Fasnakyle and Fort Augustus. This work will strengthen the network and strengthen the electricity supply to communities throughout the north of Scotland.’’

A spokesman for Scottish Power said that work was well advanced on the final section to Denny and would be completed by November as scheduled.

But many campaigned against the whole project, not least Helen McDade, head of policy at the wild land charity the John Muir Trust. She said,

" Lessons need to be learned from the Beauly Denny project about how large infrastructure is considered, and how the environment is valued. Although the developers said consistently at the Public Inquiry that the new line would not be any more intrusive than the old smaller line, I doubt anyone looking at the 200 feet tall pylons will conclude that.

"The special landscape of the Highlands, including wild areas like the Corrieyairack Pass and the Cairngorms National Park, have been significantly impacted because objectors evidence wasn't given due consideration. The John Muir Trust believes that there needs to be a National Energy Commission with independent experts involved to achieve a coherent network with economic but also social and environmental aspects properly considered."

Anti-wind farm campaigner Lyndsey Ward said Beauly to Denny could well turn out to be one of the most expensive errors the Scottish Government has ever made. "With wind farm subsidies confirmed as ceasing it is extremely doubtful that this crime against the environment was ever needed. At £600m it has cost the consumer nearly twice as much as expected. "