The proposed third runway at Heathrow may break climate change laws if “other sectors” do not cut emissions, an independent body has warned the government.

Lord Deben, chairman of the Committee on Climate Change (CCC), said he had “concerns” about how the Department for Transport had presented its case for expanding the hub in relation to greenhouse gas emissions.

The plans have come under fire over the potential to hit air quality for millions of people living near Britain's busiest airport, and the CCC warned the proposals could also have a much wider impact on industry.

The government announced it had chosen to expand Heathrow over other schemes in October following a review by the Airports Commission.

In a letter to Business Secretary Greg Clark, Lord Deben said: "The Committee has concerns about how it (the Department for Transport) presented the implications for greenhouse gas emissions from aviation in that business case."

The CCC has advised the government that, in order to stay within environment laws, emissions from air travel in 2050 should not exceed 2005 levels.

Former Richmond Park MP Zac Goldsmith reiterated his belief that Heathrow expansion could not be reconciled with air pollution limits already set.

He said: “It will be a noise disaster for over a million people and now the country’s leading voice on climate change has warned that it will be impossible under the government’s climate change legislation.

“We must and, with the right campaign, will win this battle.”

His primary rival in the Richmond Park byelection, Liberal Democrat Sarah Olney, described the proposed third runway as a “step backwards” in the fight against climate change.

Lib Dem leader Tim Farron added: “This is yet more evidence that the Tories don’t care about our environment and that the vote blue, go green slogans have been consigned to the bin.”

The CCC said it expects advances in technology to help to reduce emissions while air travel grows.

There has been an 11 per cent increase in demand in the last decade, although the latest data showed emissions are currently lower than in 2005.

However the government's plan for Heathrow estimates that emissions from aviation will rise by 15 per cent as demand surges by 60 per cent by 2050.

Lord Deben wrote: "The committee is now concerned that there is scope for misunderstanding of the Department for Transport's position based on the business case for a third runway at Heathrow.

"Using the Government's publications, it is not possible to assess whether the investment makes sense when emissions conform to the planning assumption."

Lord Debden warned that plans to expand Heathrow while keeping current targets meant "all sectors would have to prepare for correspondingly higher emission reductions by 2050".

He wrote: "My committee has limited confidence about the options for other sectors to go beyond these levels by 2050.”

The Department for Business, Energy and Industrial Strategy told BBC News the Government agreed with the Airports Commission's assessment that a new runway at Heathrow will not breach emissions targets.

A spokesman said: "We are considering how we will continue to reduce our emissions across the economy through the 2020s and will set this out in our emissions reduction plan, which will send an important signal to the markets, businesses and investors.

"Our commitment to meeting our Climate Change Act target of an at least 80% emissions reduction below 1990 levels by 2050 is as strong as ever."