Defence giant BAE Systems is to consult on 1775 potential job losses across its naval ships business, but the Clyde shipbuilding yards at Govan and Scotstoun will stay open.

Around 835 jobs are under threat in Scotland next year, at the two Glasgow yards and at Rosyth in Fife, and a further 940 roles in Portsmouth.

Shipbuilding operations will end at the Hampshire dockyard in the second half of next year, but an engineering team will be retained to support the new Type 26 warships, which will be built in Glasgow.

Govan will build hulls for the Type 26 frigates expected to be ordered by the Government, with Scotstoun doing the fitting out work.

BAE said it remained committed to continued investment in Portsmouth as the centre of its maritime services and high-end naval equipment and combat systems businesses.

The company said it was being hit by a "significant" reduction in workload following the peak of activity on the current aircraft carrier programme.

BAE said: "Following detailed discussions about how best to sustain the long-term capability to deliver complex warships, BAE Systems has agreed with the UK Ministry of Defence that Glasgow would be the most effective location for the manufacture of the future Type 26 ships.

"Consequently, and subject to consultation with trade union representatives, the company proposes to consolidate its shipbuilding operations in Glasgow with investments in facilities to create a world-class capability, positioning it to deliver an affordable Type 26 programme for the Royal Navy.

"The cost of the restructuring will be borne by the Ministry of Defence. The implementation of these restructuring activities will sustain BAE Systems' capability to deliver complex warships for the Royal Navy and secure the employment of thousands of highly skilled employees across the UK."

The grim news was given to workers at a series of meetings at 11am across the affected sites, before they were allowed to go home for the rest of the day.

Prime Minister David Cameron's official spokesman told a regular Westminster media briefing: "These are decisions taken in the UK's national interest."

Asked whether the desire to encourage Scots to vote No in next year's independence referendum had played any part in the decision, the spokesman said: "This is a Government that always takes decisions based on the national interest.

"This decision was taken with a view of how we have the best-equipped, best-maintained Royal Navy. That is the basis on which it was taken."

Asked whether any contingency plans had been made to preserve shipbuilding capacity in the rump UK in the case of Scotland voting for independence, the spokesman said: "The basis on which we proceed is on the basis that we are confident that the case (for Scotland to stay in the UK) will be successfully made."

The consequence of the decision was that "we have Portsmouth as the home of the Royal Navy fleet... and world-class shipbuilding of Royal Navy ships continuing on the Clyde", said the spokesman.

The MoD announced it is to commission three new ocean-going offshore patrol vessels for the Royal Navy, to be built by the BAE yards on the Clyde in Scotland.

The deal provides work for the company between the completion of the current aircraft carrier contract and the start of the Type 26.

Defence Secretary Philip Hammond also announced that more than £100m will be invested in the naval base at Portsmouth, which will be home to both HMS Queen Elizabeth and HMS Prince of Wales.

The money will expand the dockyard so it is ready for the ships, as well as the Type 45 destroyers which are based in Portsmouth.

Mr Hammond said: "This deal will provide the Royal Navy with three brand-new maritime patrol vessels with a wide range of capabilities which will support our national interests and those of our overseas territories.

"This is an investment not only in three ships but in this country's warship building industry. It prevents workers standing idle and sustains the vital skills needed to build the planned Type 26 frigate in the future.

"I am also pleased to announce additional investment in Portsmouth Naval Base to prepare for the significant increase in tonnage as the home port for the Royal Navy's aircraft carriers and destroyers."

Admiral Sir George Zambellas, First Sea Lord, said: "These new patrol vessels will build on the proven performance of the River Class by adding a flight deck to take the Navy's Merlin helicopters and by adding operational flexibility through extra storage capacity and accommodation. They are very welcome."

There was no immediate comment from Portsmouth North MP Penny Mordaunt, who was recently appointed as a Commons aide to the Defence Secretary.

But the move was attacked as a politically-motivated "act of lunacy" by one of the city's Conservative councillors.

Alistair Thompson said: "This is devastating for the workers and their families but also for all those people involved in the supply chain that keeps the dockyard working.

"Many of those who I represent as a councillor are hugely concerned that this decision has been taken for political reasons because of the referendum in Scotland next year.

"It makes no sense to close England's most advanced ship-building facilities. It is an act of lunacy that could make us reliant on foreign shipyards for the supplying of the Royal Navy.

"The other point is that this causes irreparable damage not only to the country's ability to build new ships but also maintain them. The jobs that are being lost are highly skilled and once they are gone it will take years to build them back up.

"This is something that the Government should realise. It is certainly something BAE know as they encountered this problem when shipbuilding moved back to the city only a few years ago."

Gerald Vernon-Jackson, leader of Portsmouth City Council, said: "I condemn the decision to shut down the last remaining shipyard in England with the capability to build advanced surface warships.

"This decision is bad for Portsmouth, with the loss of many highly-skilled jobs, but it's also bad for the defence of the UK and for the Royal Navy.

"The remaining yards with the capability to build advanced warships are in Scotland, and the referendum on Scottish independence is less than one year away. Ministers have put the defence of the UK and the future of the navy at real risk.

"We will work as hard as we can to protect jobs in Portsmouth. Portsmouth remains the home of the Royal Navy, with more than 10,000 jobs remaining in the dockyard."

Labour leader Ed Miliband said: "I deeply regret the job losses we've seen. It is a terrible blow for the workers and for their families.

"The priority now is to do everything we can to help those people find alternative employment and to help their families.

"We will be working with the Government to try and make that happen that's really important and a big priority.

"I do welcome the decision that's been made to preserve work both in Portsmouth and in Scotland.

"Britain has a proud shipbuilding past. We need a shipbuilding future for the Royal Navy."