A German company was told that ministers had probably decided against the Tyneside yard early this year and pulled out of talks.
A letter from Dr Friedrich Hennemann, of Bremer, the German shipbuilding company, said the Government decided not to award the critical order for the Royal Fleet Auxiliary vessel Sir Bedivere to Swan Hunter in January.
The French company CMN finally walked away from negotiations to buy the complex on Monday, in the wake of a decision to grant the contract to Rosyth Royal Dockyard in Scotland.
The letter was revealed by Jim Egan, national officer of the Amalgamated Engineering and Electrical Union, during an emergency debate.
He said the document was proof that the Government had 'consistently lied' over the future of the yard, which employs nearly 700 workers.
Closure of the plant could increase unemployment on Tyneside by nearly 10,000.Reuse content