OPPONENTS of the controversial Beauly-Denny powerline have called for alternatives to be reconsidered after it emerged the project's cost has almost doubled.
The overall bill for the 137-mile line to take renewable energy from the Highlands to the central belt has risen from 323 million to nearer 600m in seven years.
The project, which aims to replace the existing 132kV line with a 400kV overhead line, was approved by energy minister Jim Mather last year despite widespread opposition from environmental campaigners. the decision followed a lengthy public inquiry in 2007.
Last night the Scottish Government insisted the powerline remained vital to its flagship renewables drive.
But Helen McDade, head of policy for the John Muir Trust, said: "The economics alone make it vital to reconsider, but we shouldn't lose sight of the fact that this line will lead to wanton destruction of the Highland landscape.
"Given that the energy regulator Ofgem is increasingly recognising that sensitive landscapes need to be given more consideration when planning transmission routes, it would be ironic if Scotland remained stuck with this white elephant."
A Scottish Government spokeswoman said that investment in infrastructure was vital to achieving its target of generating 100 per cent of Scotland's electricity needs from renewables by 2020.
• Analysis: Too much focus on budget overshoot misses the bigger picture - we need this line for the future
"Beauly-Denny is essential to harness the vast renewable potential in the north of Scotland. The initial costs of the Beauly-Denny project refer to 2004 figures and have been subject to revision over time and we understand that estimated costs have increased due to the detailed engineering studies.
"The costs of transmission represent 4 per cent of an average domestic bill and it is for the regulator to determine what costs can be passed to consumers.
"The long-term enhancements to the grid are a necessary part of the development of a secure, affordable and sustainable fuel mix and a low-carbon future."
Scottish & Southern Energy's (SSE's) estimate for its section of the route was 245.2m in 2004. It has now told Ofgem the construction costs have risen to 473.3m, although the regulator has restricted the investment to 458m.
ScottishPower, which is responsible for a 12-mile section of the line in Stirlingshire, says its costs have risen from 77.7m to at least 100m.
The rising costs have been attributed to the delay in getting to the construction stage, the increased cost of the raw materials needed, particularly steel, and measures imposed by the government to mitigate against environmental damage which were not factored in to the original estimates.
Ofgem, however, says that the cost rises affecting the project will have little impact on consumers who will have to pay just 10p a year extra for the next 20 years as transmission costs make up only a very small part of a domestic bill.
SSE says preliminary work is already under way on the project, with full construction on the replacement line, including the erection of new pylons, ready to begin later this year. It is due for completion in 2014.
A SSE spokeswoman said: "The original estimate did not include a rise in the cost of raw materials, improvements in safety and construction standards and additional costs of rationalisation schemes and mitigation schemes which were imposed on SSE as a 'condition' of the consent."
The mitigation schemes include taking down about 68 miles of existing overhead transmission line in the Highland and Perth and Kinross areas, in addition to the existing 137-mile Beauly-Denny overhead line, which is being removed at a cost of over 50m.
ScottishPower is still in discussions over what mitigation measures it needs to carry out, which could further increase its costs.
The Scottish Government and campaigners have been putting pressure on the company to bury part of the electricity line around Stirling, although it has so far resisted.
A ScottishPower spokesman said: "This is a very important part of Scotland's future energy infrastructure.
"It will play a vital role in bringing new green energy from the north of Scotland to the Central Belt and open up the developing energies of wave and tidal as well on onshore wind."
Ofgem confirmed it was consulting on allowing SSE extra funding for the Beauly-Denny project, but that it reduced the amount asked for from 473m to 458m.
A spokesman said: "We had independent consultants look at it and we think they can do it more efficiently. That's our job, to ensure that whenever companies put in requests for funding we have a good hard look and the costs are adequate for what the company needs but fair in terms of what the customer should pay for.
"But although these are very large sums of money, the cost to the domestic customer is very small. Even with SSE's extra funding it would only increase an electricity customer's bill by 10p per year over 20 years."The Beauly-Denny project was given the go-ahead following a pubic inquiry spread over 11 months and costing an estimated 10m.
By the time it ended, two and a half years had passed since Scottish Hydro Electric Transmission (SHETL), a subsidiary of SSE, and SP Transmission, a subsidiary of ScottishPower, published the proposed route for the new line.