High Court judges will hear a legal challenge over controversial plans to expand Heathrow Airport next year.

A coalition of councils, residents, environmental charities and the mayor of London Sadiq Khan are challenging the Government's decision to approve the building of a third runway.

At a hearing on Thursday (October 4), Mr Justice Holgate dealt with preliminary issues in the case, which is due to be heard over two weeks in March.

The case is being brought against Transport Secretary Chris Grayling by local authorities and residents in London affected by the expansion and charities including Friends of the Earth and Plan B.

Protesters gather outside the Royal Courts of Justice, as legal action over plans to expand Heathrow is launched

The coalition claims the government's National Policy Statement (NPS) setting out its support for the project fails to properly deal with the impact on air quality, climate change, noise and congestion.

A spokesman for Mr Khan said: "One of the mayor's top priorities is cleaning up the toxic air in our city which causes thousands of premature deaths every year.

"He is greatly concerned about the impact of a third runway on air quality, noise pollution and also on public transport."

Before the hearing, a crowd of about 50 demonstrators gathered outside court to hear speeches from prominent opponents of the expansion including shadow chancellor John McDonnell and Green Party co-leader Jonathan Bartley.

Shadow chancellor John McDonnell speaks outside the Royal Courts of Justice

Mr McDonnell, whose Hayes and Harlington constituency is one of those affected by the plans, said up to 4,000 homes could be damaged or lost if the third runway goes ahead.

"It isn't just our homes, it isn't just our community, this is our planet itself," he added.

"This will be such a retrograde step in the campaign that we have to ensure climate change is halted."

Support from Labour MPs helped push through the proposals to expand Europe's busiest airport with an overwhelming majority of 296 in a Commons vote last month.

Mr Grayling said the new runway would set a "clear path to our future as a global nation in the post-Brexit world".

Construction could begin in 2021, with the third runway operational by 2026.

Mr McDonnell said up to 4,000 homes could be damaged or lost if the third runway goes ahead

Oliver Hayes, climate change campaigner at Friends of the Earth, said: "Heathrow is already the single biggest source of emissions in the UK.

"Adding a third runway will make it virtually impossible for us to meet our climate change targets and demonstrates a shocking willingness to leave future generations stranded with climate-damaging infrastructure."

Plan B director Tim Crosland said: "The broad coalition of devolved government and civil society lining up against the government is proof that this is not a political issue, it's a coalition for the future of life on earth - one that everyone can get behind."

An aeroplane takes off over the rooftops of nearby houses at Heathrow Airport in Harmondsworth

A Department for Transport spokeswoman said: "Expansion at Heathrow is a critical programme which will provide a boost to the economy, increase our international links and create tens of thousands of new jobs.

"As with any major infrastructure project, we have been anticipating legal challenges and will robustly defend our position.

"Today's hearing does not impact on the work Heathrow is undertaking on its application for planning consent or the timetable to deliver this much-needed runway."

A Heathrow spokeswoman said: "We are participating in the legal challenges as an interested party given our role as the promoter of this critically important, national project.

"Our work in delivering Britain's new runway will continue in tandem with this process following overwhelming support in Parliament.

"We remain focused on the work needed for our development consent order submission in 2020 and we are getting on with the delivery of this project which will benefit the whole of the UK."