The Royal Mail's private underground railway system could eventually be used in the construction of London's much-anticipated east-west rail link.
Mail Rail, which runs for 6.5 miles under central London, is to close this month, as part of a Royal Mail cost-cutting drive.
Post bosses say they have been talking to interested parties about possible alternative uses for the 75-year-old system.
But another prospect - that of using the tunnels and track in the construction of the £11bn CrossRail project - could also be on the table, it has emerged.
"Mail Rail has always been part of the plan," a CrossRail spokesman told BBC News Online.
He said informal discussions had already taken place with the Royal Mail.
But he stressed it would "not be appropriate" to begin formal talks until CrossRail is given the green light by the government.
"Although the route of Mail Rail doesn't precisely lend itself to being converted into CrossRail, there are elements of it which could be used," the spokesman said.
"They (The Royal Mail) are aware of our interest, and they know what our intentions are," he added.
"But there have been no formal discussions."
No final decision
A government decision on the fate of the CrossRail project is expected "within a few weeks", according to CrossRail spokesman.
The scheme, which would link Heathrow airport in the west with Stratford in the east was first mooted in the early 1990s.
It would be the largest UK transport project in a generation.
But although Strategic Rail Authority (SRA) and Transport for London (Tfl) are making the business case for the project, no final decision has been taken on the route.
Six alternatives are currently on the table - ranging in cost from £3.3bn to £11bn.
But all use a central London core route, from Paddington to Liverpool Street, similar to that currently used by Mail Rail.
Using Mail Rail as part of the CrossRail project was the most popular suggestion made by BBC News Online users, following our initial story on the closure of the system.
Other ideas included a transport museum, using it to transport rubbish for recycling or delivering food to the homeless.