The future of shipbuilding on the Lower Clyde can only be saved if the Scottish Executive steps in and places an order with the last remaining yard to prevent its closure, union leaders warned yesterday.

The workforce of Ferguson Shipbuilders, the only commercial shipyard left on the Clyde, was told yesterday that four out of five are facing redundancy as the order book is empty.

Management at the Port Glasgow yard has entered into a 30-day consultation with staff and confirmed that 99 of the 126 jobs at the yard are threatened.

Workers have been told that management is looking to lose 86 manual and 13 technical and managerial workers.

That would leave a workforce of just 27 at the 104-year-old yard. Managers have let the staff know that if any want to go voluntarily they can leave immediately, but warned that involuntary redundancies are an inevitability.

Final outfitting work is being carried out on the Loch Shira in the yard's Newark Quay but when the £4.6m passenger ferry is handed over to its owner CalMac Ferries next month there will be no work left at Ferguson.

The only other jobs which the yard has on its books are small steel fabrication or repair work.

Ferguson previously bid to build a £14m fisheries protection vessel but was turned down in early 2006 in preference to Appledore in Devon.

However, concerns were raised about the tendering process and last May the Scottish Fisheries Protection Agency (SFPA) froze the deal and launched an investigation.

The SFPA will not re-tender until that review is finalised, which will be August at the earliest, four months after work on the Loch Shira is complete.

Alex Logan, a plater at the yard and the acting convener of the GMB union, said a contract from the executive for a fisheries protection vessel is all that can save Ferguson.

Mr Logan, who joined the yard as an apprentice 31 years ago, said the executive must intervene immediately and bring forward the order.

He said: "We are not giving up without a fight here. We will do everything to keep our people in jobs. This town cannot afford to lose Ferguson and we have no choice but to fight this."

Robert Breckenridge, of the Amicus union, who works in the yard's pipe fabrication unit, said: "Because we have already tendered for this job all the preparation work is done.

"If we got the go-ahead we could start cutting the steel tomorrow. That's how ready we are to take on this job."

Jim Moohan, chairman of the Confederation of Shipbuilding and Engineering Unions, said Ferguson needed the order for the new fisheries protection vessel.

He said: "This could give the consultation period major substance. Without any action the executive is, in effect, placing a closure sign upon the yard.

"This order is in the hands of the Scottish Executive."

The only politician to contact the workers personally to offer support was Trish Godman, the Labour MSP for West Renfrewshire.

Richard Deane, managing director of the yard, said: "We have been continuing to restructure the company - this is by no means a closure. The number of redundancies has not been decided yet."

A spokesman for the Scottish Executive said that until the SFPA had finished a review of its internal procedures it would not re-tender the fisheries vessel contract.

Meanwhile, as workers at Ferguson prepared for a bleak future, Des McNulty, the Deputy Communities Minister, announced £3.7m of investment for Inverclyde.

The funding will enable Riverside Inverclyde, the new urban regeneration company, to support a range of local projects, including the removal of the James Watt Dock wall to allow visual access to the waterfront and the redevelopment of the upper floor of the Port Glasgow town buildings.