The disclosure will embarrass Malcolm Rifkind, Secretary of State for Defence, who told the Commons on Thursday that only 450 of the 3,700 jobs would be lost because of the decision to allocate 12 years of guaranteed work on surface ships to the Fife yard.
In a BBC Radio interview yesterday, he said the figure of 450 had been agreed with Babcock Thorn, operators of Rosyth and described the 'scaremongering claims' of both Rosyth and Devonport, which won the contract, that there would be tens of thousands of job losses as nonsense.
However, Allan Smith, managing director of Babcock Thorn, said the first time he had heard mention of the figure of 450 job losses was during Mr Rifkind's Commons speech.
He said: 'It would not be correct to say we agreed that figure. Rosyth never gave precise figures, nor agreed to precise figures.' Mr Smith said 1,000 would be nearer the company's estimate. There was a 'magnitude of error' in Mr Rifkind's claim.
John MacDougall, leader of Fife regional council, said last night that the workforce could be cut by 1,500 over the next two years unless additional work was found.
The full political effect of the Government's decision to go back on its 1984 promise of giving the Trident work to Rosyth has yet to be felt.
Some Scottish Tories believe the Government's decision is potentially lethal to any hope of a continued Tory revival in Scotland. Mr Rifkind's claim to have worked with Rosyth on estimating the unemployment effects, when in fact there was no consultation, will not have helped to pacify critics who maintain the decision was entirely political.
The Plymouth yard, according to Mr Rifkind, had undercut Rosyth's proposal by pounds 64m. To keep the Scottish yard in business, he proposed to allocate 12 years of guaranteed work on surface ships - 18 contracts in total, including two aircraft carriers, Type-42 destroyers, mine warfare ships, and Type-22 and Type-23 frigates.
Union leaders at Rosyth say that although managers believe the guaranteed contracts will give them time to develop new expertise and to successfully compete beyond the protected years, they have been given little more surface ship work than they have at present. Although initially optimistic about Mr Rifkind's guarantees, Mr Smith appeared less hopeful yesterday that Rosyth could rely on the Government's word. He said: 'I don't believe this, or any other government, can give 12-year guarantees. Governments change. Commitments disappear.'
In Devonport, where Mr Rifkind estimated the job losses to be 350, Mike Leece, the managing director of DML, which operates the yard, did not rule out attempting to take over Rosyth when the present naval dockyard contracts run out next year.