Concerns that a third runway at Heathrow would undermine efforts to meet the UK’s legally binding emissions targets have been raised by a government advisor.

Lord Deben, chairman of the committee on climate change, has written to business secretary Greg Clark about the issue.

The peer, a former Conservative environment secretary, identifies a potential serious flaw in the Department for Transport’s business case for building the third runway, The Times reported.

He told Clark that the report, published last month, included a “central case” in which aviation emissions would rise 15% above a previously agreed limit as a result of building the runway.

The committee had previously advised ministers that a new runway could be built without breaching UK climate targets as long as emissions from aviation did not rise above 2005 levels by 2050.

The UK has bound itself under the Climate Change Act 2008 to cut its emissions by 80% on 1990 levels by 2050.

Lord Deben’s letter reminded Clark that the committee’s recommended cap on aviation emissions at 2005 levels already assumed drastic cuts by other sectors of the economy in order to meet Britain’s overall target.

Removing that cap to accommodate the third runway would require even deeper emissions cuts elsewhere, which could prove impossible to deliver.

“My committee has limited confidence about the options for other sectors to go beyond these levels by 2050,” he wrote.

Lord Deben noted that the government was due to publish the detailed case for the runway early next year, around the same time as a plan for meeting its climate target. He made clear his concern that the two plans could be contradictory.

A government spokesman told the newspaper: “The government agrees with the Airports Commission’s assessment that a new runway at Heathrow can be delivered within the UK’s carbon obligations,” adding: “Our commitment to meeting our Climate Change Act target is as strong as ever.”