Ferrovial revealed late on Tuesday that French private equity firm Ardian and The Public Investment Fund (PIF), run by the Saudi crown prince Mohammed bin Salman, would take stakes of 15% and 10% respectively.

It added that the agreements remained subject to regulatory clearance and rights that could be exercised by other shareholders in Heathrow's parent firm FGP Topco.

They include the Qatar Investment Authority and the Australian Retirement Trust.

Ferrovial, a Spain-based infrastructure specialist, once had a majority holding of almost 56% but has gradually reduced its interest since 2012.

Its holding has remained steady at 25% for the past 10 years.

It had warned about a threat to investment at Britain's hub airport after the Civil Aviation Authority (CAA) ruled the airport must cut the fees it charges airlines for the period 2024 to 2026.

The per passenger fee, which is passed on in the price of an airline ticket, has been a source of great anger for Heathrow and airlines alike.

The latter have long accused the CAA of allowing Heathrow to overcharge customers while the airport argues it needs more cash to spend on improving the customer experience.

The airport is currently loss-making but losses have narrowed this year as passenger numbers return to levels seen before the COVID pandemic, which grounded the vast majority of global air traffic for extended periods.

Heathrow recently reported receiving 59.4 million passengers in the first nine months of this year, up 34.4% from 2022.

Ferrovial, which hopes to complete the deal within six months, said it remained fully committed to continuing to invest in its other airport interests.

Ferrovial has a 50% stake in Aberdeen, Glasgow and Southampton airports and owns 49% of Terminal One at New York City's JFK airport.

Luke Bugeja, CEO of Ferrovial Airports, said: "Over the last 17 years, we have been contributing to Heathrow's transformation, together with our fellow shareholders, achieving some excellent milestones throughout our long-term role as investor.

"These include overseeing an investment of £12bn, expanding its capacity with the construction of Terminal 2, and improving its operational performance.

"We are very pleased to have made Heathrow one of the world's most connected airports and the busiest airport in Europe."

Analysts at Banco Sabadell said the deal would allow Ferrovial to invest in new projects with more attractive returns than at Heathrow.

Ferrovial shares were up 2.5% when markets opened on Wednesday.