SNP and Labour MPs have joined forces to call for major new infrastructure they believe can secure Clyde shipbuilding for a century.

Politicians from both the city’s main parties have expressed growing concern over the UK Government’s embryonic proposals to inject competition in to the totemic industry.

They still believe that Westminster could save money by funding now dropped plans build a £200m-£300m “frigate factory” in Glasgow - or even constructing a truly world-class £1bn facility similar to those developed overseas.

The SNP’s Chris Stephens and Labour’s newly-elected Paul Sweeney, a former worker at Clyde yards owner BAE Systems, stress such investment would still be lower than the cost of a single ship currently on order.

Mr Sweeney said: “The Clyde needs £1bn to be really world-class. That would set the Clyde up for a century. The Government could pay for this, perhaps through loans, and get its money back through cheaper, better ships for our navy.”

Paul Sweeney MP

The Herald: Paul Sweeney

The Glasgow North-East MP added that the previous plans for a frigate factory, of perhaps £200m, would have gone some way to make the Clyde competitive.

As The Herald has revealed BAE Systems Naval Ships managing director Iain Stevenson has acknowledged such a factory would have been “wonderful” but could not be funded.

Mr Stevenson has a more modest - but still substantial £100m investment under way - to enable his yards, Govan and Scotstoun, to build eight highly sophisticated Type 26 frigates.

Iain Stevenson

The Herald: GLASGOW, SCOTLAND - AUGUST 31: Iain Stevenson (Managing Director of BAE Systems Navel Ships) poses for a photograph in front of the Offshore Patrol Vessel HMS Forth under construction in a dock at BAE Systems Scotstoun shipyard on August 31, 2016 in Glasg

Just three Type 26s will cost £3.7bn, 10 times more than a purpose-built shed for their manufacture.

It is not clear, however, whether the Clyde will get orders for another five less expensive Type 31 frigates.

Mr Stevenson said BAE Systems was interested in such work - especially engineering and design for the vessels - but warned that talk of up-front pricing and competition could see a “race to the bottom”.

No UK shipyard has built a ship of this size on its own in recent decades apart from BAE Systems, previously seen as the UK’s sole strategic builder.

BACKGROUND: Will anybody ever build Type-31 frigates?

Now it will likely have to compete under a new shipbuilding strategy to be announced soon. The strategy is based on a paper by Sir John Parker which suggested sharing warship shipbuilding and encourages “block” construction - where yards each built parts of a vessel.

The SNP’s Mr Stephens echoed Clyde concerns about Type 31s programme. He said: “Along with other MPs, I have been concerned for some time over the lack of detail, purpose and capability of the Type 31 frigate. “

Chris Stephens MP

The Herald: GLASGOW, SCOTLAND - MAY 06: Still Game Barman Boably the Barman aka Gavin Mitchell poses for a photograph in the Old Govan Arms with SNP Glasgow South West candidate Chris Stephens and Humza Yousaf on May 06, 2015 in Glasgow, Scotland. (Photo by Jamie Sim

The Glasgow South-West MP is seeking a Westminster debate on the strategy amid concerns that the Parker report included claims, such as no one yard can build two types of ships at once, contradicted by industry practice.

He added: “The shipyards with the capacity, skills, and workforce to build Type 31 frigates are to be found on the Clyde.”

Union convenor Duncan McPhee has previous expressed “disappointment” with the failure to deliver the frigate factory.

He fears competition will discourage investment. “We don’t want a return to the old days when two yards competed for the same small order and the one which lost went bust.”

There has been speculation that BAE Systems - assuming it wants or can cope with the order - would have to compete with sometime rival and sometime partner Babcock International.

However, Mr McPhee and Mr Stevenson and Scottish politicians do see some prospect of the two firms working together, on a potential order for two giant 40,000 tonne supply ships needed for Britain's two new aircraft carriers, both the product of joint working.

The two big ships are not "complex warships" and the British Government has previously placed orders for such vessels overseas. Tankers - "oilers" - are currently being made in Korea.

HMS Queen Elizabeth under construction at Rosyth

The Herald: The Red Arrows fly over as Queen Elizabeth II officially names Royal Navy's new aircraft carrier HMS Queen Elizabeth during a visit to Rosyth dockyard in Scotland. PRESS ASSOCIATION Photo. Picture date: Friday July 4, 2014. See PA story DEFENCE Carrie

However, the ships they navy needs - called "fleet solid support" or FSS" - are far more sophisticated than average cargo vessels and are armed.

Mr Stevenson of BAE Systems said the British may open bidding internationally. But he stressed putting the new ships together with the Type 31s might create a meaningful order that could be shared.

He said: "The world has changed. Brexit has happened. We should build FSS in the UK. I think so if you want to build UK shipbuilding back up again you have to put volume through."

The FSS, however, are too big for the Upper Clyde. Babcock's Rosyth dockyard - where the two carriers were assembled - is a more obvious candidate.

Mr Sweeney, meanwhile, still hopes to see investment back at the old Inchgreen shipyard in Greenock, a little-used site big enough for the kind of giant covered yard Germany and other states have developed.

The derelict Swan Hunter yard on the Tyne

The Herald: FORMER GLORIES: Cranes at the dormant Swan Hunter shipyard, on Tyneside, wait to be  shipped to India

Union leaders remember when the Scotstoun yard had to fight Swan Hunter in Wallsend on the Tyne for the Type 23 frigates which both Type 25 and Type 31 are to replace. The English yard went in to receivership in 1993 as it worked on the last three Type 23s.

The UK Government has said both its strategy and the Type 31 concept will be revealed soon.