Heathrow’s decades-long ambition to add a third runway received a fresh jolt on 9 March when airline giant International Airlines Group (IAG) cautioned investors that the £49 billion project could leave the airport with ‘empty concrete’ unless costs are capped at £30 billion.
In a note reported by financial outlet AInvest, IAG argued that spiralling construction and financing expenses would force Heathrow to hike landing charges, driving airlines – and connecting traffic – to rival European hubs. The warning lands just as the Civil Aviation Authority opens a second consultation on how early-stage costs from 2025-26 can be recouped, a decision that will determine whether the private-finance model survives without taxpayer support.

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The Government formally endorsed the expansion last month, claiming it could unlock 30 new destinations and add 0.4 per cent to GDP. Yet environmental groups and several cross-party MPs say moving the M25 and increasing flight movements by a third are incompatible with the UK’s carbon-reduction targets. With planning consent unlikely before 2029, today’s intervention by the airport’s largest customer underscores the political and financial tightrope ahead.
For global-mobility managers the runway debate matters because Heathrow’s capacity constraints already make securing peak-season seats – and compliant cargo slots for pets and lab equipment – a planning nightmare. A delay or downsizing of the scheme would entrench slot scarcity and could push more long-haul corporate traffic through Paris or Amsterdam, complicating duty-of-care routings and increasing short-haul legs within Europe’s new Entry/Exit biometric system.