Ferry companies Stena Line and P&O have abandoned plans for a new multi-million pounds shared terminal in south west Scotland to serve Irish Sea routes.
Plans for the harbour extension have been shelved
Escalating costs have been blamed for the decision to pull the plug on the new joint facilities at Cairnryan.
Stena had planned to move its base about six miles up Loch Ryan from Stranraer to Cairnryan where rivals P&O already operate.
The move was intended to allow the redevelopment of Stranraer seafront.
Stena and P&O have been talking about the shared re-development of Cairnryan Port for more than four years.
The joint venture was given the go-ahead earlier this year by a harbour empowerment order.
Plans were well advanced with work due to start soon and the new terminal scheduled for opening in 2009.
A statement from the two companies said it was "simply no longer economically viable" to proceed with the shared port facilities for Irish Sea services.
The greater impact is on Stena who had sought to move from outdated facilities at Stranraer to cut the journey time of sailings to Belfast and reduce fuel costs.
Route director Alan Gordon said they would now review their options which include staying at Stranraer or going it alone with the development of a new terminal further up Loch Ryan.
P&O spokesman Terry Cairns said it was business as usual for them.
The decision has consequences for ambitions plans by Scottish Enterprise Dumfries and Galloway and the local council to re-develop the waterfront area of Stranraer when the ferries had gone.
Galloway and Upper Nithsdale MSP Alex Fergusson said a lot of hard work had "effectively been wasted".
Mr Fergusson said it was vital to ensure that Stena Line remained in Dumfries and Galloway as its presence was "vitally important".
"I will be seeking urgent discussions with the management of Stena to explore the company's future intentions," he said.
He added that he would do everything possible to ensure the firm remained part of the region's transport infrastructure.
"An awful lot of hard work, consultation and compromise has now effectively been wasted," he said.
"The important thing now is to ensure Stena's future in Loch Ryan as part of the Euroroute to Northern Ireland."
South of Scotland SNP MSP Alasdair Morgan voiced concern at the wider impact of the decision.
"Clearly this announcement is very disappointing, not least because of the potential impact that it will have on plans for the regeneration of Stranraer waterfront," he said.
"It is very much to be hoped that those parts of the scheme which are not dependent on the Stena move can still go ahead."
Dumfries and Galloway MP Russell Brown said the project was vital for the area.
"It's absolutely essential that all the partners work together to seek to ensure Stena does retain its ferry port on Loch Ryan and that it relocates up the loch," he said.
"If this does not happen the implications are potentially devastating.
"Many local jobs could be jeopardised and the whole regeneration project for Stranraer and the surrounding area could be under threat."