Heathrow construction projects run 61% over budget, new review finds
Construction costs at Heathrow Airport have come under fresh scrutiny after an independent review found that a sample of major capital projects completed or delivered between 2019 and 2024 came in significantly above their original budgets.
The review, commissioned by the UK Civil Aviation Authority (CAA) and carried out by transport and infrastructure consultancy Steer, examined 13 projects that had been flagged for additional scrutiny. The projects had an estimated combined cost of around £943 million, but their final or forecast cost rose to approximately £1.52 billion — 61% above the original estimate.
One of the most significant examples highlighted in reporting on the review is Heathrow’s main entrance tunnel. The project is reported to be 276% over its original budget and around a decade behind its initial schedule.
The findings come at a particularly important time for Heathrow, which is seeking approval for its proposed third runway and wider £49 billion expansion programme. The scale of the existing cost overruns has intensified questions about how future major construction works will be estimated, managed and monitored.
The issue has also created tension between Heathrow and the airlines operating from the airport. Airlines have argued that passengers could ultimately bear part of the cost of construction overruns through higher airport charges. The review’s recommendations on how much of the additional cost should be recovered from Heathrow have therefore attracted significant industry attention.
For the wider UK construction sector, the Heathrow case highlights one of the industry’s most persistent challenges: maintaining accurate cost and programme forecasts on complex projects where design changes, inflation, procurement difficulties and unforeseen site conditions can quickly increase the final bill.
The CAA is continuing its consultation on the findings, with the current consultation deadline set for 25 September 2026.
Key figures
- 61% — reported average cost overrun across the reviewed projects
- £943m — original estimated cost
- £1.52bn — final/forecast cost
- 13 — projects examined in the Steer review
- £49bn — proposed Heathrow expansion programme
Source: UK Civil Aviation Authority / Steer
