WORKERS in Clyde shipyards will become the victims of an "absolute betrayal" if delays in orders to build Royal Navy frigates lead to redundancies, Nicola Sturgeon has warned.

The UK Government insisted that eight type-26 warships would still be constructed at BAE Systems facilities on the Clyde, however, Philip Dunne, the defence minister, said no timeline for building them would be confirmed until the end of the year and refused to rule out redundancies as a result of the setbacks.

Unions have reacted with outrage and threats of large-scale industrial action after claiming they have been told that original plans to start work this month had been delayed until the end of 2017 and that the time it will take to build the ships had been lengthened meaning fewer workers would be needed to complete the orders.

The GMB Union said it would allow two aircraft carriers, which have been put together in Rosyth and cost more than £6 billion, to rust if just one Clyde-based worker is put out of work.

The row, which saw the First Minister visit yards in Govan and Scotstoun to hear the concerns of workers, came as the UK Government was accused of betraying pre-referendum commitments when the frigate contracts were promised to the Scottish yard if the country voted No, and voters were told rejecting independence would protect thousands of shipbuilding jobs.

The SNP leader wrote to David Cameron, pointing out that an original commitment to build 13 ships had already been cut to eight and called for a "clear guarantee" the construction would proceed as promised and that there would be a constant supply of work. She added: "Anything less would be an absolute betrayal of the commitments made to the workers at the shipyard."

The GMB union has claimed that 800 jobs could go at the Govan and Scotstoun yards if work on the eight anti-submarine frigates is delayed. The union said it had been told during briefings by BAE Systems last Thursday that work on the new frigates would not now begin until 2017.

Gary Cook, Scottish Regional Organiser for the GMB Union, described anger and resentment among workers after saying they had been promised a long-term future. He claimed union representatives had been told the yards would now have 18 months to build each frigate, while they would previously been told it would take just a year.

He added: "We should be thinking about starting to cut steel now for the first type-26. Instead of that, it's been delayed until the end of next year, there's a massive gap in the program.

"They've delayed the type-26, they now only want one every 18 months which means the rate of work through the yards is not going to be sufficient, it will result in 50 per cent of the workforce being thrown on the industrial scrapheap.

"We will not accept one further compulsory redundancy on the upper Clyde. I want the Government to hear that loud and clear. We will do whatever it takes. We've got two aircraft carriers that have not been handed over yet. As far as we're concerned it'll rust in Rosyth if there are any compulsory redundancies on the Clyde."

David Mundell, the Scottish Secretary, said the UK Government is "absolutely committed" to shipbuilding on the Clyde and the type-26 programme, claiming there would be jobs in the industry for years to come, which was only possible as Scotland had stayed in the UK.

However, he did not give a guarantee that no jobs would be lost due to a slippage in the timetable. He said: "Over the next decade we will spend around £8 billion on Royal Navy warships. We will also build two new offshore patrol vessels on the Clyde, maintaining Scottish shipbuilding capability ahead of the start of the type 26 build."

Mr Dunne also refused to rule out redundancies on the Clyde under questioning from MPs but said he wanted to assure shipyard workers that the UK Government "remains committed" to the Type 26 programme.

But he said he could not confirm when building work on the frigates would begin. The minister suggested that it would not be until 2017 at the earliest, as the timetable will only be set out in a new national strategy published before the end of this year.

Asked by SNP MP Tommy Sheppard if he could give a commitment that there will be no compulsory redundancies on the Clyde as a result of delays to the programme, Mr Dunne said: "All I can say to you and to the workforce on the Clyde is that we have... a commitment to build eight Type 26s on the Clyde and that will provide work for the highly skilled workforce on the Clyde for many, many years."

The SNP’s defence spokesman Brendan O’Hara accused ministers of preparing to renege on promises made to Scots before the independence referendum.

Chris Stephens, the SNP MP whose constituency covers the shipyards, hit out at Mr Dunne’s description of a meeting with unions last week as "routine".

Mr Stephens said that an event in which workers were informed that up to 800 jobs could be lost was "not a routine meeting by any standards".

Labour’s shadow defence secretary Emily Thornberry also rounded on the Defence Secretary Michael Fallon accusing him of being missing in action.

She told MPs that he could not "be seen for dust", despite the controversy.

Mr Thornberry accused ministers of setting the scene for a "Tory betrayal of Scotland.. And one that the SNP will not be able to fix".

Mr Dunne hit back accusing Labour of "seeking to make political capital" just days before the Holyrood elections.

No 10 sources accused the SNP of "gross hypocrisy" and said that if Scotland had become independent no UK warships would be being built on the Clyde.