GMB Scotland warned David Cameron yesterday that the Royal Navy’s new flagship supercarriers can “rust at Rosyth” if any compulsory redundancies are made over the delayed contract for new naval frigates.

The union has mooted the idea that shipyard workers could hold the two supercarriers hostage in port to halt any forced job losses at the BAE yard on the Clyde.

GMB Scotland officer Gary Cook said that the joint unions at Rosyth, Govan and Scotstoun were prepared to do “whatever it takes” to defend jobs.

He said: “We have got two aircraft carriers that have not been handed over yet at Rosyth.

“As far as we’re concerned they will rust at Rosyth if there are any compulsory redundancies on the Clyde,” although he said that the decision was ultimately one for the joint shop stewards’ committee.

Unions are furious over delays to the Type 26 frigate that could threaten up to 800 jobs at the Glasgow yards.

Mr Cook said: “The worst-case scenario is that we will lose 800 jobs and, ironically, if that happens then 20 per cent of the work will have to be outsourced to yards south of the border.

“BAE Systems would be irreparably damaged and it would probably signal the death knell of complex warships being built on the Clyde and therefore the UK.”

“I usually have a half-full kind of attitude, but this is do or die for the Clyde. We need to go back to the original plan, get this ship factory up and running, bring this date forward to start cutting the first Type 26 to January or February.”

Unite national officer Ian Waddell warned defence ministers not to underestimate the workers’ “anger or the feeling of betrayal” and said workers would “use everything in their armoury to defend the UK’s historic ability to design and build its own warships.”