Defence Secretary John Healey put forward the case for a third runway at Heathrow Airport on economic growth grounds, as Prime Minister Andy Burnham stopped short of committing to a position on the expansion plans.

Addressing delegates at the IMF gatherings convened in Bangkok, Healey put forward the view that expanding airport capacity — Heathrow among the projects cited — had played a notable role in driving employment and economic activity over the past several decades. Reeves, who held the role before him, had placed Heathrow expansion at the centre of the case that Britain remained an attractive destination for investment.

Burnham, however, expressed reservations about the proposal, telling a broadcaster that responsibility for the matter rested with London and its residents. The airport's chief executive had made remarks earlier in the week, describing the absence of a third runway at the country's most trafficked hub as an opportunity that would be lost.

Plans for a third runway at Heathrow have been contested for years, drawing pushback from nearby communities, elected officials, and those concerned about environmental impact. Reeves put the government's backing behind the expansion the previous year, stating that an additional runway had become a necessity and that the decision was no longer one the government could set aside.

When the project came up in questioning a month ago, Burnham positioned the matter as one for London to resolve, stating that the views of people there ought to be heard before any decision is taken. He went on to say that moving straight into action on the back of the consultation would not be the appropriate path.

Following the close of its public consultation on the National Policy Statement — the document that underpins any decision on whether a new runway at Heathrow should be approved — the Department for Transport indicated that it was reviewing what actions to take next. Healey told reporters that those matters were under active review, with additional decisions and announcements to be made in due course.

Formal backing from Burnham is what the airport's ownership group has indicated it requires before the year closes, with that commitment seen as a condition for the project to move forward. In an appearance on a broadcast news programme earlier this week, airport chief executive Thomas Woldbye indicated that clarity on the government's stance toward the project would be welcome.

Woldbye expressed hope that the prime minister would support the project, and argued that a third runway's advantages would extend well beyond London, pointing to a supply chain stretching from one end of the UK to the other as evidence of its nationwide reach.

Equipped with four passenger terminals and a pair of runways, Heathrow handles the travel needs of over 80 million people annually. Building a third runway would lift the annual flight ceiling from its present 480,000 to as many as 720,000 — an average of roughly 2,000 departures and arrivals per day.

Carrying a cost estimate of £33bn, the scheme would require the demolition of hundreds of homes, the rerouting of rivers, and the construction of a tunnel to carry the M25 motorway between junctions 14 and 15. Heathrow has indicated that the third runway, originally pencilled in for 2035 once planning consent was obtained, now looks unlikely to become operational until 2039, with approval processes and regulatory hurdles cited as the reasons behind the four-year slip.