Heathrow will later this year submit its final planning application for the construction of a third runway, having been forced to delay the expected completion date by a year when the UK’s aviation regulator capped the amount that could be spent in the early phases of the project.

The London airport’s operator announced today that it would run an eight-week public consultation between April and June to help finalise its expansion proposals. Responses from the consultation will feed into the final planning application, which the operator says will be submitted to the Planning Inspectorate “towards the end of 2020”.

Heathrow Airport said last month that it now expects to complete its third runway between early 2028 and late 2029 instead of in 2026, as previously targeted. This followed a review of expansion costs by the UK Civil Aviation Authority, which concluded that a “modest delay” to the third runway’s completion would be preferable to the higher early construction costs that would be incurred by targeting a 2026 opening.

The CAA noted in its December report that in order to retain the 2026 target Heathrow had said it would need to bring forward the timing of certain spending, and that total early costs would need to be about £2.9 billion (in 2014 prices), made up of £500 million in planning costs (or Category B costs) and £2.4 billion in early construction costs (or Category C costs).

The regulator does not want passengers to bear the brunt of early spending costs for a project that has yet to secure planning permission.

Heathrow says that its final planning application will detail how it can expand while meeting the requirements set out in the UK’s Airports National Policy Statement. The document will also “restate Heathrow’s commitment to ensuring an expanded Heathrow meets strict environmental targets, delivers tens of thousands of new high-skilled jobs and honours our commitments to local communities”, says the airport’s operator.

But there is a big question mark over whether Heathrow’s proposed expansion can align with the UK’s pledge to bring greenhouse-gas emissions to net zero by 2050. Environmental campaigners argue that expanding the country’s biggest airport is not conducive to meeting the net-zero target.

Heathrow says it will announce dates and locations for consultation events in the coming weeks.

“This country is ready for a decade of infrastructure delivery underpinned by expansion at Heathrow,” states the airport’s director for expansion, Emma Gilthorpe. “We are keen to ensure our plans continue to be supported and shaped by local people as we prepare to deliver the economic boost Britain needs.”