PLANS for the tallest wind turbines in the mainland UK are to go ahead while the battle over a controversial Highland project took a new twist when Scotland's natural heritage body made a last-minute objection.

Seven of the 15 turbines at the development, less than two miles north of Crawfordjohn in South Lanarkshire, will be 500ft - more than double the height of the Scott Monument in Edinburgh.

It is expected the structures will be visible to motorists on the nearby M74.

The project's backers, who have now gained planning consent following a lengthy consultation, say the 15 turbines at Middle Muir could power up to 28,000 homes.

Banks Renewables insisted that despite the turbines' height they will not damage the beauty of the surrounding scenery.

Colin Anderson, development director, said: "Middle Muir wind farm is not only sympathetic to its surrounding landscape, but will directly support the communities in which it will sit."

It is hoped the farm will create between 25 and 50 jobs and generate community benefit funding of £7.2 million over its lifetime, according to the Scottish Government.

Energy Minister Fergus Ewing said: "Once it is up and running the wind farm will help reduce carbon emissions from our electricity generation, aiding Scotland's work to tackle climate change.

"Wind farms like Middle Muir play an important part in helping Scotland reach its target of the equivalent of 100% of electricity demand generated from renewables."

Meanwhile, developers behind one of the most controversial wind-farm proposals in Scotland say they are deeply frustrated by a last-minute objection from Scottish Natural Heritage (SNH) based on wild-land concerns.

RWE Innogy UK wants to build 31 turbines at Allt Duine, where the closest turbine would be less than one mile from the Cairngorms National Park boundary.

It has been widely opposed by recreational and conservation groups, including Ramblers Scotland, the John Muir Trust and the Mountaineering Council of Scotland. Until now SNH has not objected.

The company insists the turbines would be shielded by a ridge line that forms the boundary, and that because of the carefully designed layout, the wind farm would not be visible from the A9 or Kincraig, Kingussie or Aviemore.

All await a ministerial decision on the development, but Jenny Gascoigne, RWE's wind development manager Scotland, said: "Over the past four years, SNH has consistently maintained its 'no objection' to the Allt Duine scheme. It is both disappointing and concerning that SNH has now objected at this late stage."

John Uttley, SNH's principal adviser for its planning and renewables unit, said that when the agency gave advice to the government on the farm before the public inquiry in 2012, it was at the edge of a large area it was considering classifying as wild land.

He said it subsequently improved its approach to mapping wild land and published a new map in June, which supports the new Scottish Planning Policy. This offers "significant protection" to "wild land as shown on the 2014 SNH map of wild-land areas".

He said that the changes meant it was now "appropriate" to object.