Heathrow could have to spend nearly £2bn on property insulation if a third runway is built, according to anti-expansion campaigners.

Opponents Hacan have claimed the £700m figure Heathrow said it will put aside to insulate 160,000 homes could be a lot more.

Chairman John Stewart said: “Heathrow are offering to insulate many more properties than they do today.

“Our supporters welcome this but only if their homes will be fully insulated.

“The cost of doing that would run into billions.

“Admittedly, our estimates are based on costs for an individual home and there would be discounts if an order was placed, but it will still cost substantially more than the £700m originally put forward.”

Mr Stewart added that the average semi-detached house will cost about £11,800 to totally insulate a property against noise.

A Heathrow spokesman said: "Heathrow’s noise insulation scheme is privately funded and has been created following several years of public meetings in our local boroughs and after receiving feedback from more than 2,000 residents.

"We recognise that our expansion plans need to treat people fairly, and so we extended our noise insulation offer to all homes based on the 55 decibel noise contour, the preferred measure of noise used by the European Union and the Mayor of London.  

"Heathrow’s plans for expansion can be delivered on time and on budget.

"In fact, Heathrow already has a strong track record in this regard, having invested £11bn over the past decade on transforming the airport building Terminal 2 and Terminal 5."