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North Southwark and Bermondsey MP Simon Hughes said plans to stop services on the South London Line were "contrary to all logic".
The service, which runs from Victoria to London Bridge, is due to stop in 2012 because of changes taking place at London Bridge as part of the ongoing Thameslink upgrade.
Mr Hughes said the loss of the service would affect thousands of people living and working in his constituency and other south London boroughs.
Transport Minister Chris Mole said the Department for Transport had set out plans for a replacement service between Victoria and Bellingham, but that Transport for London had made the decision not to implement it.