Anger is growing over the return of the east coast mainline to private hands after it emerged that it had generated £1bn for UK taxpayers since 2009.

The east coast mainline paid a record £235m back to the government in its final full year as a state-owned company, a 12% increase on the previous year. That means the franchise, run by Directly Operated Railways (DOR), has returned more than £1bn to the public purse over the past five years, sparking renewed calls for it to remain in public ownership.

The RMT transport union said the figures made "a mockery of the government's plans to bulldoze through a reprivatisation before the next election, ignoring the financial and operational success of DOR and the catastrophic impact of two previous private sector failures on the line".

The London to Scotland rail franchise has been under the control of the Department for Transport since the previous private sector operator, National Express, pulled out in 2009. In 2007, another private company GNER also ceased its east coast operation after its parent company Sea Containers ran into financial difficulties.

The Department for Transport said the decision to return the line to private sector ownership was final. The government has received bids from three private sector companies to take over the franchise: FirstGroup; Keolis which is part of the French state-owned SNCF, in a joint venture with Eurostar ;and a joint bid from Stagecoach and Virgin Trains. It will announce the winner will be announced in November and hand over the operation of the line in March next year.