If those opposed to the expansion of Gatwick airport have their green fields and areas of outstanding natural beauty as talismans, those standing in the way of Heathrow can point to a 600-year-old barn.

Harmondsworth Barn — once dubbed the Cathedral of Middlesex by the late poet laureate Sir John Betjeman — is a Grade I-listed building in the ancient village of Harmondsworth, which is likely to be destroyed as part of contentious plans to build a northwest runway at the UK’s largest airport.

The plan would see the airport’s boundary come almost to the centre of the village, with everything south of that line demolished.

While the barn will be saved, as well as the mid-11th century St Mary’s Church, campaigners say they would be so close to the airport that the church would have no congregation and the barn would be pounded by noise and fuel fumes.

The destruction of a village that dates back to the 6th century will be one of several obstacles facing Heathrow after it got the nod from Sir Howard Davies on Wednesday in the conclusion to his three-year inquiry on where to build a new runway in southeast England.

The other option to expand Heathrow — a plan put forward by Jock Lowe, a former Concorde pilot and senior British Airways executive — would save the village by extending the existing northern runway west over the M25. However, Sir Howard rejected this plan on Wednesday, which was the surprise inclusion on a shortlist of three options to increase airport capacity in the southeast of England, alongside a second runway at Gatwick.

But despite its beauty, Harmondsworth’s fate will fall well behind concerns over air quality and strong opposition from Conservative MPs whose constituents live under the flight paths in and out of the airport, which would get busier whatever of the two options were chosen.

“Air pollution could potentially be a showstopper for Heathrow,” says Angus Walker, partner in the planning and infrastructure team at Bircham Dyson Bell.

“This is because of the way the EU air-quality laws are set up. A new project in [one] part of a country cannot slow down achievement of air-quality targets in that part of the country. It is going to be difficult for Heathrow to argue that it will not make air quality worse in the London region.”

In April the Supreme Court ruled that Britain must speed up its efforts to tackle air pollution, having breached EU limits. This is where Heathrow is more vulnerable than its rival Gatwick, given the EU limits on pollution are breached on some roads around the airport.

A previous government decision to allow a third runway at Heathrow was overturned by the courts in 2010 on environmental grounds. To avoid this happening again, the Airports Commission was forced to open a last-minute public consultation on air quality in May.

“Heathrow is particularly bad because of where it is: it is between two motorways and a heavily built-up area. You don’t have the same problem at Gatwick,” says Anna Heslop, an environmental lawyer at ClientEarth.

Noise levels could prove another battleground, according to John Stewart, chair of Hacan, the leading protest group against the expansion of Heathrow airport. “Noise is not so much a legal problem but a big political problem,” he says. “All the people under the flight path . . . are all voters. Many more people are affected by noise from Heathrow than any other airport in Europe.”

The government would also face strong opposition to Heathrow from within its own ranks, ranging from Boris Johnson, London mayor and MP for Uxbridge, to Justine Greening, development secretary.

“It is the question of resistance and opposition,” says John Strickland, an aviation analyst at JLS Consulting. “It is going to be there in a forceable way. When you have got big-gun MPs with extremely well-heeled constituencies who have enormous influence, then that’s a big challenge.”

Even though Heathrow has won the first battle, its backers know they still have a hard fight. They intend to make a public case by pointing out how their proposal has changed since it was pulled by the coalition in 2010. That setback had “forced the company to come up with something that can actually be built”, said one person close to the situation.

The original plan threatened to destroy more picturesque villages, including a significant part of the village of Harlington with its 1,000-year-old yew tree and Norman church. The airport’s proposal has moved the new runway further to the west to run over the M25. This would allow aircraft to fly higher and over motorway on approach and take-off to minimise disruption to residential areas, the person said. The yew tree and the church will both be saved.

However, there is still the significant hurdle of air-quality breaches on the M4. Heathrow is counting on the fact that something will have to be done regardless of expansion given the Supreme Court’s ruling this year.

Supporters have proposed measures that Sir Howard has accepted would mitigate the impact of expansion — providing they are implemented, which requires the London mayor to agree. These include creating a low-emissions zone that would ban vehicles using older diesel engines from that part of the motorway.

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