The decision has angered locals who believe the 125m tall structures will be a blot on the landscape and hugely detrimental to the tourism industry.
Nick Blezard, chairman of the Save Northumberland's Environment (SANE) protest group, said: "I think the decision is outrageous.
"We are very surprised because we thought the historical setting and the impact of the turbines on the landscape would have been sufficient for it to be refused.
"It seems the planning inspector has completely missed the point. The turbines will be clearly visible from beauty spots such as Bamburgh, Newton-by-the-Sea and Ros Castle but the inspector doesn't seem to have grasped that."
Their one glimmer of hope is that npower renewables must now prove the turbines will not have an impact on the radar system at nearby Brizlee Wood.
This follows an objection to the scheme from the Ministry of Defence on the basis that the structures would interfere with the air defence radar and jeopardise national security.
Npower renewables has been given five years to come up with a solution which must be cleared by the Secretary of State for Defence, but officials remains confident of coming up with an answer.
Plans for a wind farm at Middlemoor were first announced in 2004. Npower renewables initially proposed 25 turbines but scaled it down to 18 following public consultation.
It was referred to the Department of Trade and Industry (DTI) because of its size - it is the biggest of the five existing proposals in north Northumberland and the applicants say it will power over 27,000 homes.
The wind farm covers parts of both Berwick and Alnwick districts but falls into the jurisdiction of the latter. It was consulted on the proposals by the DTI and lodged a formal objection.
As a result, a three-week public inquiry was held in Alnwick last November and now the Department for Business Enterprise and Regulatory Reform has granted consent.
Clare Wilson, npower renewables regional development manager, said: "Renewable energy technologies, such as wind, are essential to cutting UK carbon emissions, and given our excellent resources, the UK can become a world leader, securing our energy supply and creating many thousands of new UK jobs.
"Of course, we will continue to work with local communities, and are committed to substantial efforts to protect and where possible enhance the environment.
"We are delighted that John Hutton and Malcolm Wicks have decided that we can construct and operate the Middlemoor windfarm."
Protesters are now worried that the public inquiry starting on September 16 into the proposed wind farm at nearby Wandylaw could be a 'fait accompli'.
The inquiry has been called following Berwick Borough Council's rejection - and RidgeWind's subsequent appeal - of plans for a 10-turbine scheme just two miles north of Middlemoor.
Inspector Alan Novitsky, in his comments on Middlemoor, said: "The renewable energy background to the proposal is so strong, and the potential benefits so great, that the harm identified to visual aspects and the settings should not prevent the proposal from proceeding.
"The cumulative effect of the Middlemoor wind farm, were the Wandylaw scheme already in place, would be to increase the harm arising in both these spheres compared to that arising from the Middlemoor development on its own.
"Nevertheless, I consider it still insufficient to halt the proposal, although serious consideration should be given to regrouping the schemes' array of turbines into clearly separated blocks, to lessen the impact."
While energy secretary John Hutton noted that Wandylaw is not an approved scheme and that the inquiry could not be pre-judged, he noted the inspector's comments that the increased harm would still be insufficient to halt the Middlemoor proposal. In the circumstances he felt it was not appropriate for npower renewables to have to regroup its turbine proposals.
But Mr Blezard said: "What seems remarkable to me is that the inspector almost seems to be giving a decision on Wandylaw as well.
"It's particularly galling that the decision comes at this time, just as we are preparing our proofs for the Wandylaw inquiry which have to be submitted by the end of next week."
MEANWHILE, an extraordinary meeting of Berwick Borough Council's planning committee will take place on Thursday, August 21 at 6.30pm at the William Elder Building, Berwick in the wake of the Middlemoor appeal decision.
The only item on the agenda will be about the Wandylaw windfarm appeal and councillors will meet in private session, which means that the meeting will not be open to the public or the press.
The item is private to enable members to hear from counsel on the implications of the Middlemoor windfarm decision for the Wandylaw appeal.
The outcome of the private meeting will then be discussed in public at the next ordinary planning committee meeting on Tuesday, September 2.