The airport’s chief executive John Holland-Kaye reportedly stated that he had “no reason to believe” that any issues had been raised in the research conducted this year by the Department for Transport into air quality around Heathrow.

“Everything we have seen suggests that it won’t be an issue. I suspect if it were we would know about that by now,” he is reportedly told the Guardian.

Holland-Kaye added that a recent independent study by Cambridge researchers into air quality had strengthened Heathrow’s case, because he said pollution studies had not considered further mitigation measures that Heathrow had put in place to counter pollution impact from car traffic.

“What was once seen as a difficult political decision is becoming a much easier one,” he added.

The BBC has also been told by Whitehall sources that expansion at Heathrow is the purported clear front-runner.

It comes amid news that the prime minister is to suspend an announcement on airport expansion by a further week to enable cabinet ministers to express their views.

However Theresa May is understood to want to hear the opinions of colleagues.

The issue is expected to be discussed today, but no final decision is expected until October 25.

The Cabinet has both strong opponents and supporters for expansion at the west London airport.

Foreign secretary Boris Johnson has long been opposed to expansion at Heathrow. Education secretary Justine Greening is also opposed.

Meanwhile pro-Heathrow supporters include international trade secretary Liam Fox and communities secretary Sajid Javid.