Former defence secretary John Reid has warned that UK warships will not be built in Scotland if it votes for independence in next year's referendum.
His comments come after defence giant BAE Systems announced that 1,775 jobs will go across the UK.
Shipbuilding will end at Portsmouth in the second half of next year and h undreds of jobs will be lost in Scotland at the Govan and Scotstoun yards in Glasgow as well as at Rosyth in Fife.
But work on the new Type 26 vessels is earmarked for the Glasgow yards, giving workers there a vital lifeline.
UK Government ministers have already hinted that this work could go elsewhere if people in Scotland vote Yes to independence next September, though Scotland's Deputy First Minister Nicola Sturgeon has insisted Clyde shipyards could still build the ships.
Lord Reid said that UK warships would not be built north of the border if Scotland left the UK and became a foreign country.
Writing in the Scottish Sunday Express, he said: "The wider lesson from the last few days is that the only way to secure the future of Scotland's shipyards is to remain in the UK. This is not a matter of political opinion, it is a matter of fact.
"It is a fact that since the Second World War no UK Government of any political stripe has ever commissioned the building of a warship in a foreign country. It is a fact that for security, as well as economic and political, reasons we build these ships here at home in the UK."
He added: "In short, we don't build warships abroad now - and what's left of the UK wouldn't do so if Scotland separated."
BAE said there will be 835 redundancies in Glasgow, Rosyth and Filton, near Bristol, and the remaining 940 in Portsmouth.
More detail about the job losses is expected to emerge from talks between the company and unions early this week.
The war of words between Ms Sturgeon and Scottish Secretary Alistair Carmichael escalated today as he called on her to admit she is wrong on her assertion that an independent Scotland could still build UK warships.
He said: " Nicola Sturgeon is looking pretty isolated on this. The best thing she could do is admit that she is wrong.
"Is she really saying that everyone else is wrong and she is right? Is she telling us that the people who build the warships and the people who place the contracts know less about this than she does?"
He added: " The future of the Clyde yards is sustainable as part of a large and successful United Kingdom. Brilliant workers and the best complex warships in the world, it is a great combination and we should not break it."
Ms Sturgeon rebuffed suggestions that Scottish yards would not get the work if the country leaves the UK.
She said: "The simple fact is that the decision to close Portsmouth will leave the Clyde as the only place on these shores with the capacity to build naval surface ships - and that decision is testament to the world-class skills of the workers at the Clyde yards."
She added: "Our support for the Clyde is unconditional, whatever the people decide next year - as the shop steward of the Govan yard has demanded it should be - but the support of Mr Carmichael and his colleagues seems conditional on Scots doing what Westminster wants.
"The Scottish Secretary needs to tell people - does he support this work staying on the Clyde whatever the result of next year's referendum or is he actively engaged in undermining the future of one of our great industries?"
Ms Sturgeon and Finance Secretary John Swinney met BAE Systems directors and union officials in Glasgow on Friday and discussed what the Scottish Government can do to help those losing their jobs.