The public consultation over plans to expand London Heathrow airport has been reopened, after the Department for Transport (DfT) published a series of new reports analysing the impact of expanding the hub.

The new evidence includes an air quality plan and an updated noise analysis, and suggests that plans to expand Britain's largest airport will have a negative impact on air quality, noise levels and biodiversity in the area.

More on Heathrow expansion

According to the appraisal, a second runway at London Gatwick airport would have a more contained impact than a third runway at Heathrow, warning the proposal could be jeopardised unless it includes measures to significantly reduce the impact on air quality.

As a result, the consultation over the draft airports national policy statement (NPS), which sets out the government's support for expanding Heathrow, will now run until 19 December, after having originally closed in May.

"This is an important consultation and I encourage everybody to get involved across the UK," said Chris Grayling, the transport secretary.

Grayling, however, noted the case for expanding the West London hub remained as strong as ever and the DfT is aiming to publish the final proposal for expansion in the first half of next year for a vote in parliament.

Should the proposal be approved, Heathrow will then submit a planning application and discuss details of the project with local communities.

"The consultation launched today is a key milestone in developing the airports NPS which will strengthen the policy framework for expanding Heathrow," said a spokesman for Heathrow airport.

"The forecasts show expanding Heathrow, the UK's only hub airport, is even more important than previously realised. A third runway will ensure Britain's place in the world as an outward looking trading nation. That's why the government has committed to a final vote on expansion in the first half of 2018."

However, according to Cait Hewitt, the deputy director of campaign group the Aviation Environment Federation, the decision to reopen the consultation spoke volumes for the doubts surrounding the case for expansion.

"It's difficult to see how this new information can avoid delaying the process," she said. "MPs and the public will need time to understand how the new forecasts impact emissions, noise and the sustainability appraisal of the project. These address fundamental questions about the project's viability and have been provided at a late stage in the process."

In October 2016, the Airports Commission approved London Heathrow's plans to build a third runway.

However, five years since the commission was established by former Prime Minister David Cameron, the controversial expansion plan has not yet been voted through parliament and the runway will not be ready until 2025.

Plans for a third runway at Heathrow were scrapped by the coalition government in 2009, while the commission warned only one runway could be built before 2030 if Britain was to comply with its climate change obligations.

Earlier this year, the Institute of Directors (IoD), which represents 30,000 UK business leaders, stressed the need for the next government to build at least another two runways, demanding that a follow-up to the Airports Commission is established.

The IoD said the urgency was motivated by the need to make up for "years of dawdling" in airport activity, which have left Britain lagging behind the rest of the European Union. Heathrow is already operating at capacity, while Gatwick is operating at capacity at peak times and London's airports are expected to be full by the mid-2030s.