Heathrow Airport has warned that its planned third runway might be delayed by four years due to planning and regulatory issues.

The government had hoped the new runway at the UK’s busiest airport, estimated to cost £49bn, would open by 2035.

But Heathrow sees this deadline as increasingly difficult to deliver without further steps to simplify the planning process. It said on Saturday that it hoped to secure planning permission by 2029 and then open the runway “within a decade”.

The Department for Transport (DfT) said the project’s timeline had “always been ambitious” and that it would continue to work with stakeholders “at pace” on the matter.

The airport said its “core scenario” had always been to open a new runway within a decade of securing planning permission.

It said it was encouraged by the chancellor’s efforts to streamline infrastructure and remove policy and regulatory bottlenecks, and promised to continue to work with ministers, airlines and stakeholders to “progress the planning application with pace”.

Former chancellor Rachel Reeves announced the government’s support for the project in January 2025, and Prime Minister Andy Burnham – who was previously critical – said he was “open-minded” about the scheme when he came to office.

Despite attracting wide opposition from environmental campaigners and local resident groups from neighbouring areas, the project is expected to create around 100,000 jobs and provide a major boost to the economy.

The expansion would mean demolishing hundreds of homes, diverting rivers, and rerouting the M25 motorway between junctions 14 and 15 through a tunnel under the new runway.

The number of flights from the airport, currently capped at 480,000 a year, could go up to 720,000 – or nearly 2,000 a day on average.

London Mayor Sadiq Khan has always opposed the project, warning of the impact on noise, air pollution and climate change.

A draft of the planning framework for the expansion was published in June this year for consultation. Once finalised, it then needs to be put to a parliamentary vote, which could reportedly be delayed until 2027.