A high-speed rail link between Heathrow and Gatwick is being considered by ministers in a bid to expand air capacity around London.
The trains, which would closely follow the route of the M25 and mostly travel underground, would enable an airport hub described as Heathwick to be created.
Supporters of the idea claim it would provide a cheaper and quicker solution than the proposed building of an airport in the Thames Estuary.
But critics say a link between Heathrow and Gatwick would face "insurmountable" challenges.
The radical scheme, reported to cost £5 billion, is to be included in the Government's review of aviation policy which will be published for consultation in the spring.
A Department for Transport spokesman said: "As part of our work on this we are seeking views on the key issues which need to be addressed, including the importance of a UK hub airport and whether it might be possible to create a virtual hub by improving connectivity between existing airports.
"This proposal will form a useful contribution to the debate and will be considered alongside all other responses."
Victoria Borwick, a member of the Greater London Authority's transport committee, said the project must be considered.
"If there's a way of helping Londoners sort out their travel needs then this should be examined," she said."It's certainly possible to be built and I was reassured by the idea it would mostly be in tunnels and hugging the route of the M25."
But a spokesman for BAA, which owns Heathrow, said the rail link would not solve the "key problem" of runway capacity. He said: "We welcome the debate on possible solutions, however a virtual hub between Heathrow and Gatwick faces seemingly insurmountable technical, operational, political and financial challenges, and would take many years to deliver. To remain competitive in the short-term we need to find ways of protecting and valuing the successful hub we already have at Heathrow."