The estimated cost of a major railway upgrade has risen to £500m, 20 times the original estimate.
The upgrade to the Ely North junction, a connection point for East Anglia with London and the Midlands, was supposed to start in 2017 but has yet to begin.
The work was originally due to cost £25m, but the BBC understands a Network Rail report found an increase in cost.
Network Rail said the original scheme “wouldn’t release the additional services” needed by rail users.
A spokeswoman added: “A far wider range of interventions is required including layout changes at Ely station, improvements to bridges, power upgrades and improvements to level crossings, in order to fully meet demands.”
The BBC has contacted the Department for Transport (DfT) for comment.
If the upgrade was to go ahead it could be possible to run more trains between Norwich and Cambridge; King’s Lynn and London; Ipswich and Peterborough, along with extra freight services between the port of Felixstowe and the Midlands.
The report is understood to reveal that as well as extra track, a new bridge will have to be built, while Ely station and the Queen Adelaide junction will need remodelling.
More than 100 level crossings in the area will also need upgrading, the report said.
In 2017 Network Rail said the work would start between 2019 and 2024.
Despite the rise in cost, the chairman of Transport East Kevin Bentley said: “We’ve got to make sure that we are still pushing for this. This is a critical junction on the east-west route.
“We have poor east-west links, we have been forgotten about, we have been under-invested in in this region. That has now got to stop.”
Network Rail said it would put its further plans to the DfT “in the spring”.