Work to electrify two railway lines could cost five times less than claimed, according to a passengers' watchdog body.
Members of the Rail Passenger Committee (RPC) are campaigning to electrify the Ashford to Hastings and Uckfield to Hurst Green lines, which are currently served by diesel trains.
The Strategic Rail Authority (SRA) told the group the cost of the work, about £154 million, was too high.
But railway engineers at Brecknell, Willis and Company say the work would really cost around £27 million.
In a letter to the passengers' group, chief engineer David Hartland said: "I have been incensed to discover the SRA has announced the cost of these two schemes is now £154million.
"After some correspondence between myself and the SRA, they are unable to justify the increase. It makes no sense."
Members of the committee have written to the SRA demanding an explanation.
A spokesman for the SRA said: "In the case of this project, it is not good sense in terms of passenger benefit. Even if the figures were to be believed there would still not be a case."
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