Government claims Heathrow expansion would add £74bn to the economy does not include the £25bn cost of improving public transport links to keep road traffic at current levels, says Richmond council.

A third Heathrow runway could cause public transport delays and cost the economy £25bn over a 60-year period, reducing the claimed benefit from expansion from £74bn to £49bn, says Richmond council.

A third runway is expected to add around 100,000 trips a day, according to figures from the Richmond Heathrow Campaign.

This would mean seven out of ten journeys to and from the airport being made by public transport, compared with four in ten in 10.

Richmond Council leader Cllr Gareth Roberts says: “The Government’s figures don’t add up.

“By understating the true costs of the infrastructure needed to cope with an additional 100,000 daily road journeys and passenger numbers double what they are today, they are inflating the claimed economic benefit from expansion.

“They also run the risk of allowing a third runway to be built without the additional public transport capacity needed. In this case Heathrow should be barred from opening the runway until the new provision is put in place.

"This is a mess that can be avoided. The Government must face up now to the hard truth that this runway is simply unbuildable on grounds of cost, increased congestion and worsening air quality.”

Campaigners are calling for guarantees that the taxpayer will not be expected to meet the costs of new rail infrastructure required for a three-runway airport.

Peter Willan of the Richmond Heathrow Campaign says: “The Government must confirm that they will not saddle the taxpayer with this £25bn funding gap. Either Heathrow pays or their customers do.

"Even a congestion charge scheme won’t get people out of their cars unless the public transport infrastructure is in place."

Richmond council is part of a four-borough alliance opposed to expansion including Wandsworth, Hillingdon and Windsor and Maidenhead Councils.