Top legal minds are already preparing the groundwork for a fight over the expansion of Bristol Airport next summer.

North Somerset Council has promised a "robust defence" of its decision to reject the scheme to boost annual passenger numbers to 12million due to the impact on the environment and neighbouring communities.

The fate of the plans will now be decided at a national level.

For many, the story is not new. A decade ago campaigners launched an ultimately unsuccessful challenge against an increase to the current cap of 10million passengers per year.

Unlike last time, the appeal will be considered at a four-week public inquiry due to start in July – allowing campaigners to bolster the council's position – and the environment is firmly on the agenda.

Bristol Green councillor Stephen Clarke from the Bristol Airport Action Network, one of the organisations that will speak at the hearing, said: "There are currently over 20 regional airports thinking about expanding. Bristol Airport is the first to go to a planning appeal. That makes it really important as a precedent.

"There are quite a lot of international organisations that are helping us.

"We have the money we need to pay for a barrister and we have various experts. We're putting together our case."

That case will focus on the environmental arguments against the expansion.

Bristol Airport said sustainable development has always been at the centre of its plans.

It plans to become carbon neutral for direct emissions by 2025 and a net zero airport by 2050, and said it had proposed a "comprehensive package of measures" to minimise the adverse environmental impacts of an additional two million passengers per annum.

Cllr Clarke said the aviation industry was relying on technological advances like electric or hydrogen power that may eventually improve fuel efficiency but will not be able to offset the extra 23,000 flights per year.

"We aren't trying to close the airport or even reduce the capacity. We're saying it's big enough," he said. "As a regional airport it shouldn't be any bigger."

Cllr Clarke said the people of North Somerset were "completely against" the expansion – out of more than 11,500 comments on the application, some 8,900 were objections.

Bath and North East Somerset Council voted last year to oppose the expansion.

So now has Bristol City Council, after mayor Marvin Rees had publicly given his support, hailing the "huge benefits" the airport's growth would bring to Bristol and the West of England.

Both councils said the expansion was "incompatible" with the climate emergency. North Somerset Council has made the same declaration, pledging to be carbon neutral by 2030.

As well as more passengers on more flights, many overnight, the plans also propose extending the seasonal silver zone car park with more than 2,700 spaces for year-round use and the construction of a multi-storey car park.

North Somerset Council refused planning permission by 18 votes to seven following a motion from Wrington ward member Cllr Steve Hogg.

He told the special planning and regulatory committee meeting on February 10: "We must weigh the benefits – which flow towards the airport, its shareholders, pension funds and those seeking a cheap holiday in the Med – against the unbearable burdens that will fall on the local community and the environment."

Recommending approval, planning officers said local authorities have little control over emissions linked to aviation.

But Cllr Hogg said: "We have direct control over the future emissions – we do that by turning down this application."

Seconder Cllr John Ley-Morgan added: "How can we achieve our ambition for carbon neutrality by 2030 if we approve this decision?"

Bristol Airport chief executive Dave Lees said at the time the refusal risked "putting the brakes" on the future growth of the region when other areas are forging ahead.

Leader Don Davies said this month North Somerset Council had assembled a team of specialist consultants to mount a "robust defence" of the authority's position, with a senior QC at the helm.

Cllr Clarke said: "Councillors gave a clear democratic message they don't want this to happen. The airport has ignored that. I think we'll be successful at appeal."

The Bristol Airport Action Network and the Parish Councils Airport Association are two organisations registered to make representations at the inquiry.

The latter – a group of 26 parishes and one town council surrounding the airport – will highlight the effect of the emissions but also consider noise, traffic, the impact on habitats and the loss of green belt land.

Backed by its members and Stop Bristol Airport Expansion it has raised £16,000 for a legal team to make its case.

Parish Councils Airport Association chair Hilary Burn said: "We can't understand why they [the airport] haven't given residents anything. You'd think after the application was refused they'd change the conditions. Everything is the same. There was no compromise from the airport. They don't listen to us. They haven't given on one point.

"There's an ecological emergency. Airport expansion just doesn't fit.

"The secretary of state has the power to recover this public inquiry – at any point in the process he can decide to make the decision.

"North Somerset MP Liam Fox has supported us and asked for the inspector to make the decision. We have a much fairer chance with the inspector."

Stop Bristol Airport Expansion mounted a legal challenge against the previous expansion after councillors were advised that climate change "was not a material consideration". A High Court judge ruled in 2011 it did not have a legally arguable case.

Ms Burn said the airport had won the argument then because the country was emerging from a recession and needed jobs.

She said with climate emergency declarations and the Paris Agreement, the environment is firmly on the agenda – and the economic case does not stack up.

"The airport doesn't need the expansion," she said. "It should remain capped at 10million passengers per year."

She said it was too early to say if this decision will go to a judicial review as they can only be raised if the process is thought to be flawed.

John Adams from the Stop Bristol Airport Expansion advisory group said it will be interesting to see if the planning inspectors stick rigidly to "outdated" legislation, or if they give weight to current context.

He said the Supreme Court's recent decision to allow a third runway at Heathrow was "ghastly" but could prevent the expansion of any regional airport because the extra emissions would consume the country's carbon allowances as it strives for net zero.

"It's very difficult to predict how the appeal will go," added Professor Adams. "We wouldn't be putting in this amount of effort if we didn't think we had a reasonable chance.

"There's fierce opposition in local communities. There's a sense that economic values could trump people's health and wellbeing.

"The airport has to review fundamentally how it goes about its practices in the 21st century."

The airport has recently submitted updated information ahead of the appeal that takes into account the impact of the pandemic. It says the growth in passenger numbers will be slower – it does not expect to reach the proposed cap of 12million annual passengers until 2030, four years later than previously forecast – but the expansion is still needed.

A spokesperson for Bristol Airport said: "The decision by North Somerset Council's planning and regulatory committee to refuse the planning application to increase Bristol Airprt's capacity from 10 to 12million passengers a year was contrary to the recommendation of the council's own planning officers.

"The decision on the application has moved to a national level and will be made by an independent planning inspector or, if the appeal is recovered, by the Government.

"The plans to expand capacity at the airport will offer passengers more routes and flights from the South West directly, create jobs, facilitate inward investment and inbound tourism, and support greener and more sustainable, regional economic growth.

"Sustainable development has always been at the centre of Bristol Airport's plans. The expansion proposals sit alongside a roadmap which sets out how the airport will achieve its ambition to become carbon neutral for direct emissions by 2025 and a net zero airport by 2050.

"A comprehensive package of measures is also proposed to minimise the adverse environmental impacts of an additional two million passengers per annum. By preventing Bristol Airport from meeting demand for air travel from within the region it serves, the council will simply exacerbate the situation which already sees millions of passengers a year from our region drive to London airports in order to fly, creating carbon emissions and congestion in the process.

"As the UK emerges from the Covid-19 pandemic it is essential that all regions of the country are given the opportunity to grow to their full potential and contribute to the national recovery effort. International trade and connectivity will become increasingly important as the UK completes its departure from the European Union – increasing aviation capacity is essential in delivering this goal."

For more information on the appeal and to comment on the latest documents, visit www.n-somerset.gov.uk/airportappeal.