Concerns have been raised that Conservative ministers are planning to slash the programme for the new Type 26 frigates, which would be a major blow for shipbuilding jobs on the Clyde.
It is understood that the original plan to order 13 of the next generation of frigates could now be reduced to as few as eight as defence ministers are forced to make savings to the budget to help pay for replacing the Trident nuclear deterrent.
Union leaders, who confirmed with Scotland on Sunday that they have raised concerns over the prospect of such a cut directly with Conservative defence minister Philip Dunne, have “heard rumours” of government plans for the Strategic Defence and Security Review (SDSR), which is expected to be published by the end of this month.
Last night the Ministry of Defence declined to deny the Type 26 frigate speculation.
Alarm bells for the project were already ringing because of the delay in the government signing the contract with defence giant BAE Systems.
The contract was meant to have been signed by the end of 2014 but the company and ministers have yet to put their signatures on the paper.
Jim Moohan, the GMB Scotland organiser for shipbuilding, said: “I raised this with Philip Dunne recently when the first steel was cut for the ships. We have certainly heard rumours that the number of ships could be reduced, which would be very serious.”
He added: “Obviously the Ministry of Defence contracts are vital for the continuation of shipbuilding work on the Clyde and at Rosyth, and if the number of ships is reduced then that means less work and potentially will lead to people being laid off.”
But he admitted the yards needed to find work from abroad. “We cannot continue to rely on the MoD,” he said.
The fraught issue of the Type 26 frigates was at the centre of the independence referendum when UK ministers promised the work for the Clyde but only on the condition that Scots voted to stay in the UK.
It was claimed at the time that the £4 billion contract would go to an English yard instead if Scots had voted for independence.
However, since the No vote in September last year the First Sea Lord, Admiral Sir George Zambellas, has threatened to take the work to France amid contract rows with BAE, although he was quickly overruled by defence secretary Michael Fallon.
Now it appears ministers may be prepared to significantly reduce the project.
A Whitehall source said: “In the SDSR discussions the question has been asked whether the navy really needs 13 frigates or whether we can get away with less, possibly as few as eight.”
SNP senior defence spokesman Brendan O’Hara raised fears that the rising cost of replacing Trident, now thought to be £160 billion, could be at the heart of the cuts to conventional forces.
He said: “There cannot be a diminution of what was promised to BAE and the workers at Scotstoun and Govan in terms of the Type 26 global combat ships.
“It is essential that the UK government makes good on its promise and that the order for the 13 frigates is fulfilled as planned.”
He pointed out that just a few months ago Fallon had promised not to reduce the military footprint in Scotland.
“It would be impossible therefore to cut back on shipbuilding at the Clyde and keep that promise,” he said.
Last night an MoD spokesman said: “We are in the final stage of the 2015 Strategic Defence and Security Review.”