Plans to introduce mobile phone coverage on the London Underground in time for the 2012 summer Olympics have been dashed.
Operators Vodafone, O2, Everything Everywhere and Three had been working with the Chinese telecoms provider Huawei and others to extend coverage on to the underground trains and stations.
However the Tube's antiquated network of narrow, low and often tunnels combined with a lack of space at stations has proved too problematic and expensive.
A source familiar with the project said as a rough rule it was 10 times more expensive to put an antenna on the tube than it was to put one in a building.
As there was no public money available for the project, the operators were willing to pay for the installation of the networks while Huawei had offered to donate part of the equipment.
The telecoms operators are thought to have already spent several millions of pounds on the project.
"As a group, we will continue to positively explore all other avenues available to us in order to provide a service at a later date," they said in a joint statement.
A Huawei spokeswoman said it was always open to any potential underground mobile network project in the future.
"We are grateful to the companies who explored the possibility of getting full mobile coverage on the Tube, although disappointed that the genuine problems encountered could not be overcome on this occasion," a statement from the Mayor of London said.
Plans for a major expansion of wi-fi coverage in Tube stations in time for the summer Games will not be affected.