Officials at London Heathrow Airport now expect a project to build a third runway to be complete by late 2029, a year later than planned.

The timetable slip follows a decision by the Civil Aviation Authority to reject a request from Heathrow to lift spending by £650 million to £2.4 billion before the project gets planning consent.

The CAA is concerned passengers will end up shouldering the cost if Heathrow does not win permission to expand – a view supported earlier this week by International Airlines Group.

In a consultation published by the CAA, it said “the best approach in the interest of consumers” is to limit certain early construction costs to £1.6 billion.

Paul Smith, group director of consumers and markets at the CAA, said: “We believe that more runway capacity at Heathrow will benefit air passengers and cargo owners.

“Its timely delivery is required to prevent future consumers experiencing higher airfares, reduced choice and lower service quality.

“However, we have also been clear that timeliness is not the only factor that is important to consumers.

“Passengers cannot be expected to bear the risk of Heathrow Airport Limited spending too much in the early phases of development, should planning permission not be granted.”

At the same time, the CAA has approved a proposal from Heathrow to increase its spending on planning costs from £265 million to £500 million.

Greeting this decision, a statement from Heathrow said: “The CAA’s announcement is an important milestone in expanding Heathrow and connecting all of Britain to global growth.

“It increases certainty for our local communities and for the job creation, increased trade and lower airfares that expansion delivers.

“We will now review the detail to ensure it will unlock the initial £1.5-2 billion of private investment over the next two years at no cost to the taxpayer.”