Planning permission should be given for both a third and fourth runway at Heathrow, according to an influential group of Conservative MPs.

The Free Enterprise Group of 39 MPs say this is the only way to preserve London’s position as a world business hub, the Financial Times reports today,

It follows suggestions yesterday that transport secretary Justine Greening is determined to find a long-term solution to the UK’s congested airports.

Replacing Heathrow as the country’s largest airport has become “a case of when, not if,” according to a Sunday Times report, quoting a Whitehall source.

Short-term solutions could include building another runway at either Birmingham, Stansted or Gatwick.

But there is a growing willingness within government to consider a new hub airport in the longer term.

Tory backbenchers Elizabeth Truss and Kwasi Kwarteng, who are among the authors of the Free Enterprise Group paper, argue that there is already private funding, industry support and existing infrastructure for developing Heathrow, but that the government should consider a more ambitious plan, the FT said.

“Britain needs in the order of at least three new runways to accommodate demand,” the report said. “Concentrating these runways in the same location allows the facility to enjoy the benefits of a hub airport.”

Another proposal put forward as part of the group’s seven solutions to boosting UK growth is the development of a “Ministry of Infrastructure”, responsible for identifying strategic infrastructure projects and arranging finance for them.

The FT also reports this morning that designers and consultants working with Lord Foster, who last year unveiled a master plan for a £20 billion four-runway airport 30 miles east of London, have devised a funding model they claim would avoid any significant increase in landing charges currently paid by airlines at Heathrow.

A further £3 billion would be needed for a rail link connecting the site to the high speed line between the Channel tunnel and St Pancras station.

Lord Foster’s team proposes taking £8 billion from the landing charges levied on airlines using Heathrow between 2018 and 2028. A further £11 billion would be raised through landing charges levied at the new airport during the decade after its opening, which is earmarked for 2028.

Meanwhile, the closure and redevelopment of Heathrow would secure £10 billion for the estuary airport. Finally, £4 billion would be obtained from the development of land around the new airport for facilities needed to support it.

Former BAA executive Mike Forster, now working with Lord Foster’s Foster + Partners, said if the government supported an estuary airport, landing charges could be frozen at 2018 levels plus inflation because Heathrow would require minimal investment thereafter.