Bridging the M25 to build Heathrow’s third runway could de-rail the airport’s expansion plan due to the scheme’s cost and complexity says International Airlines Group.

In its submission to the government’s consultation on its Airports National Policy Statement, which closes tomorrow, IAG said there’s no detailed risk and cost analysis of Heathrow’s plans to build over one of Europe’s busiest motorways.

IAG estimates bridging the M25, close to the M4 junction, would cost £2-3 billion on top of Heathrow’s £17 billion bill for the third runway.

All costs will be paid for by airlines’ customers, argues the carrier.

In its submission, IAG says that Heathrow is the best option for expansion.

However, the airport needs to focus on a shorter runway (3,200 metres rather than 3,500 metres) that doesn’t breach the M25 and is delivered to a business case that keeps current charges the same or lower than today’s.

It also welcomes credible schemes from promoters other than Heathrow.

IAG says this would ensure customers get the very best scheme, built at an affordable price, which delivers a competitive new Heathrow for the UK economy post-Brexit.

Willie Walsh, IAG chief executive, said: “Airlines were never consulted on the runway length and they can operate perfectly well from a slightly shorter runway that doesn’t cross the M25.

“Bridging the M25 means years of disruption on a motorway already plagued by delays and congestion.

“As well as increased costs, this will have a huge impact not only on motorists but on local communities around Heathrow.

“The airport has yet to produce a business plan that assesses the financial implications and risks of bridging the M25.

“We will not pay for a runway that threatens both costs and delays spiralling out of control and where critical elements of the project could be undeliverable.

“Britain needs cost-effective airport infrastructure that benefits the country rather than Heathrow’s shareholders.

“It is already the world’s most expensive hub airport and customer charges must not increase to pay for the new runway.

“We urge the government to benchmark Heathrow’s costs against other similar global schemes”.