Life is easy for the toads and bats of Staines-upon-Thames: the disused railway line has formed a woodland corridor that runs north towards Heathrow. Terminal 5 is just a mile or so further on as the bat flies. But to reach it from Staines station would take a hapless rail passenger almost two hours via three trains.

That could drop to just six minutes under plans to link Staines and other parts of Surrey to the airport. Yet as Heathrow prepares for a major consultation on its third runway on Tuesday, new rail links are just an option, despite the argument that they would help tackle the airport’s pollution problem. They would also be a clear answer to transport secretary Chris Grayling’s call for “market-led” proposals for new railway lines.

As a precondition of Heathrow expansion, parliament has stipulated that the proportion of passengers travelling to and from the airport on public transport must rise from 39% to 50%. The Department for Transport officially supports the idea of a rail link, and says it is “working closely with interested parties to progress this project”. Yet the promoters believe the schemes – a light rail plan favoured by Staines council, as well as fully integrated rail lines – have been left languishing.

Graham Cross, chief executive of Heathrow Southern Railway (HSRL), one of the proposed schemes, is frustrated. “Grayling was talking about the market coming up with ideas. Investors were interested. Now we’ve had six months of drift.”

Cross says HSRL, which is backed by US firm Aecom, doesn’t need government money for its £1.3bn-£1.6bn proposal. “But,” he adds, “the DfT does have to facilitate it.” That means a pledge that rail franchises will deliver a certain number of services to Heathrow using their line.

Standing on a bridge over the existing line from Waterloo to Windsor, Cross points to where the offshoot would go, curving round the perimeter of Staines Moor, a site of special scientific interest, into a tunnel.

The plan would, he concedes, eat up a stretch of field, and require demolition of one house and its surrounding willow trees. But the soundtrack to this bucolic scene is the extraordinary roar of the M25, at this point 12 lanes of thundering traffic, directly behind where Cross is standing.

The line running north-west from Staines was closed in the Beeching cuts and then severed by the motorway. A new link could switch three million car journeys a year to rail, “improving air quality and reducing congestion here, and bringing more jobs and investment to a town that could use a boost”, according to Cross.

And it’s not just Staines: the extension would link the airport directly to towns such as Woking, Basingstoke and Guildford, as well as London Waterloo via Clapham Junction.

Heathrow agrees that the economic and environmental benefits are clear. A spokeswoman said: “Heathrow is keen that this project is moved forward at the earliest opportunity, and we will pay our share towards the cost.”

But the airport is fighting shy. One reason is evident in faded signs in the woods, telling visitors about the wildlife on the former railway. They note plans by BAA, as Heathrow’s owner was then known, to reopen the line as Airtrack. The scheme went as far as public consultation in 2008, but when the original third runway plan was scrapped in 2010, Airtrack died too.

Still, an empty space for a station stands under Terminal 5, built in readiness for future rail links. Another part of the equation could come first: a four-mile link to the Great Western mainline, planned by Network Rail to take passengers travelling from the west to Heathrow without going into London Paddington.

Regardless, Heathrow must now convince planners that upgrades of the Piccadilly line and the eventual opening of Crossrail will meet the public transport target – along with a congestion charge on cars to encourage a “modal shift”. Critics, however, believe that the charge would need to exceed £40 to deter motorists.

Heathrow’s 12-week public consultation starts this week, outlining in detail its expansion masterplan. Over it now looms the fresh spectre of cancellation under a Boris Johnson premiership – although many expect him to shelve past opposition to the third runway. Either way, with green issues returning to the fore, investors will look to see whether the DfT will help make the rail link a reality.