A north Essex council is facing a potentially huge legal bill - conservatively expected to be in the hundreds of thousands of pounds - after Stansted Airport won an appeal case over its expansion plans.

Residents 4 Uttlesford (R4U) swept to power in 2019 at Uttlesford District Council (UDC) - toppling the incumbent Conservative administration - after taking a strong stance against the airport's plans to expand in order to serve up to 43million passengers a year.

The R4U administration, led by council leader John Lodge, overturned the council's previous stance in favour of the airport proposals to expand passenger numbers subject to conditions.

But the council has been strongly rebuked by planning inspectors for its actions.

Stansted Airport appealed and a Planning Inspectorate panel - appointed by the secretary of state and comprising Michael Boniface, GD Jones and Nick Palmer - has now given the go-ahead to Stansted's plans.

They involve two new taxiway links to the existing runway, new aircraft stands, 274,000 aircraft movements and 43m passengers a year.

In awarding costs, inspectors heavily criticised the council’s reasons for refusal as "imprecise, vague and unsubstantiated", and said the strength of evidence in favour of the proposal was "such that the application should clearly have been granted planning permission by the council".

"They do not stand up to scrutiny and there was no material difference between the position in respect of noise, air quality and carbon between its resolutions in 2018 and 2020," it said.

"The council persisted in arguing for the imposition of a condition (so called ‘condition 15’), which is clearly unlawful and fails to meet the tests contained in the National Planning Policy Framework, unnecessarily prolonging the Inquiry."

The council's reliance on "a perceived direction of travel in policy or emerging policy that may never come into being in the form anticipated is not a sound basis for making planning decisions" and an appeal should not have been necessary, inspectors said.

"The panel therefore find that unreasonable behaviour resulting in unnecessary or wasted expense, as described in the Planning Practice Guidance, has been demonstrated and that a full award of costs is justified."

Campaign group Stop Stansted Expansion was allowed to participate as a main party to the inquiry, which was held virtually because of the coronavirus pandemic.

But the planning inspector panel dismissed objections on noise, traffic and other environmental factors - and arguments over a potentially lower rate of growth of the airport.

"It remained unclear throughout the Inquiry, despite extensive evidence, why the speed of growth should matter in considering the appeal," the panel said in its written appeal decision.

"If it ultimately takes the airport longer than expected to reach anticipated levels of growth, then the corresponding environmental effects would also take longer to materialise or may reduce due to advances in technology that might occur in the meantime.

"Conversely, securing planning permission now would bring benefits associated with providing airline operators, as well as to other prospective investors, with significantly greater certainty regarding their ability to grow at Stansted, secure long-term growth deals and expand route networks, potentially including long haul routes."

The panel concluded that the climate change effects of the scheme would not be contrary to planning policy or significantly affect the government's statutory responsibilities on climate change.

"The proposed development would not have a significant or unacceptable effect on carbon/climate change," the panel said.

It added: "It is not expected that the proposed development would alter the airport’s rural context or affect nearby heritage assets in any way bearing in mind the current permitted use of the airport and its likely future use were the appeal to be dismissed."

Overall, the panel concluded that "the balance falls overwhelmingly in favour of the grant of planning permission".

"Whilst there would be a limited degree of harm arising in respect of air quality and carbon emissions, these matters are far outweighed by the benefits of the proposal and do not come close to indicating a decision other than in accordance with the development plan."

Stansted Airport managing director Steve Griffiths welcomed the decision, which followed a public inquiry.

“Throughout, the aim was to provide clarity and certainty for local communities and we feel today’s decision is a strong endorsement of our approach and the strength of the case we made at the Inquiry," he said.

“The Planning Inspectorate’s decision provides clear assurance to local communities that Stansted’s growth can be delivered in a responsible and sustainable way.

"This decision allows us, the community and our airline partners to plan ahead with certainty.

“We always believed that UDC failed to provide any credible or substantiated reasons to justify refusing the application, while ignoring the clear advice it received from its own officers and expert legal advisers, and this belief is borne out with the inspectors’ conclusion that planning permission should have been granted by the council and the appeal should not have been necessary."

A council spokesman said: “We acknowledge the planning inspectors’ decisions, although are of course disappointed. We will need to take advice on the justification given for the respective decisions, including consulting with counsel, before commenting further.”

Residents 4 Uttlesford party chair Dan Starr said: "R4U is bitterly disappointed with the appeal decision because we believe that growing Stansted Airport to the size of Gatwick is incompatible with the new UK legislation that limits emissions to well-below 1990s levels."