UPDATE 1-Holders of 35% of Heathrow plan to divest along with Ferrovial

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By Inti Landauro and Andres Gonzalez

MADRID/LONDON, Jan 16 (Reuters) - Shareholders in Heathrow accounting for a 35% stake intend to sell their shares alongside Ferrovial, the Spanish firm said on Tuesday, effectively putting on the bloc 60% of shares in one of the world's busiest airports.

Two months ago, Ferrovial agreed to sell its 25% stake in Heathrow for $3 billion to Saudi Arabia's Public Investment Fund (PIF) and Ardian in a deal that allows other shareholders to "tag-along" and divest their shares at the same price as Ferrovial.

The conditions mean that Ardian and PIF, which originally agreed to buy 15% and 10% stakes, respectively, now need to increase their planned investments in the airport or find a partner to complete the acquisition.

PIF is not interested in increasing its stake, while Ardian would be open to increasing its stake by no more than 10%, a person with knowledge of the situation said.

Ferrovial said there was no certainty that the transaction will be completed.

Heathrow Airport Holdings Limited's top shareholders are FGP Topco Limited, a consortium led by Ferrovial with 25% and the Qatar Investment Authority, which owns 20%.

Canadian pension fund Caisse de depot et placement du Québec owns 12.62%, Singapore sovereign wealth fund GIC 11.20%, Australian Retirement Trust 11.18%, China Investment Corporation 10% and Universities Superannuation Scheme also 10%.

Following the pandemic downturn, Heathrow's activity recovered to 2019 levels and it expects to handle 81.4 million passengers in 2024.

($1 = 0.7895 pounds) (Reporting by Inti Landauro and Andres Gonzalez; editing by Jason Neely and Tomasz Janowski)