UK Treasury officials are planning to cut back the cost of the Thameslink programme by £750m.
The move comes as a government cost-cutting measure in response to the recession as well as a recent "value for taxpayers' money" test conducted on the programme, according to guardian.co.uk.
The programme, originally estimated at £5.5bn, aims to provide direct trains from south-east London and Kent into the capital and beyond.
Under the cost-cutting plan, £400m could be saved from the carriage order by reducing it to 950 units, £150m by removing the automatic train operating technology and £200m by redesigning the development work around London Bridge station, which is a major interchange.
According to the report, the £16bn Crossrail project may also undergo similar cutbacks.