A row over the future of one of Scotland's major ports is set to come to a head in the coming weeks in a landmark battle over private control of a public asset - the sea itself.

At the heart of the standoff with the public Cromarty Forth Port Authority (CFPA) is an application by the marine engineering firm Global Energy for control over the Nigg Energy Park and part of the shipping lane at the mouth of the Cromarty Firth.

The £472 million-turnover Global Energy Group (GEG) is a poster boy of Highland industry that has served as a useful backdrop for Scottish Government announcements on job creation. Since 2011, it has received more than £9m from Highlands and Islands Enterprise (HIE) to redevelop the yard and the quayside. The region's biggest employer is now ­threatening to withhold £20m of ­investment in further harbour ­development if its ­application to the ­Scottish Government is not successful.

At a fiery public meeting in Invergordon last month organised by the Cromarty Firth Action Group, an avowedly neutral community discussion forum, Global's chief executive Iain MacGregor accused the CFPA of misleading the public and "scaremongering" over Global's plans.

CFPA's chief executive Bob Buskie countered that Global was trying to create a "ransom strip" that would give it total control of the entry to the Cromarty Firth, threatening the inland port of Invergordon's engineering and cruise-liner tourism business.

The port authority has also appeared to raise the quasi-political and economic-nationalist dimension of the standoff, dog-whistling towards the sometimes-obsessive Scottish concern with public ownership of our natural assets. GEG is quarter-owned by the Japanese marine engineering giant, Matsui.

Inverness-based economist Tony Mackay told the Sunday Herald: "I am not sure of the real reasons for the dispute but it is giving the Cromarty Firth a bad image. There seem to be some big egos involved."

Mackay points to the Danish company Semco Maritime and the international energy services company Rigmar, which have recently set up operations at the Invergordon base. "Those companies are competing with Global Energy in some markets and that may be one of the reasons for the fallout," said Mackay.

One local business leader notes that CFPA's former chief executive and harbourmaster Ken Gray, who retired from the port authority in June 2013 after eight years' service, is now working for "the enemy" at Nigg as Global Energy's marine director. The uncomfortably ­intimate nature of the bust-up is further enhanced by the fact that CFPA's ­chairman Sandy Cumming, a former head of HIE, worked hand-in-glove with Global as it rose to become a major local employer and recipient of public funds.

If Scottish ministers approve Global's plans, it would mean shipping in and out of the Cromarty Firth, as well as ­investment decisions, would be controlled by two separate port authorities, one public and one private.

A green light would also mark the first time a public port asset was forced to give up either land or sea to a private company to set up a "rival" business, although - despite sources close to CFPA accusing it of seeking to "privatise the sea" - the marine portion would continue to be owned by the Crown Estate, a state quango.

Since 1973, all shipping in and around the firth has been controlled by the CFPA. Global is now insisting it must control all operations on the 700,000 square metre Nigg yard as well as 600,000sqm of water at the mouth of the firth, amounting to less than 1% of the sea area of the firth. Such control would, Global claims, free it from the obligation to seek CFPA's permission to carry out dredging or other improvement work, saving time and money.

Also, control of the land would, for the first time, allow it to offer customers "fast and efficient berthing that rivals ­international competitors". It would also allow "larger rigs and vessels to transit safely" into its port and quayside area.

But the CFPA, whose case depends heavily on claims it has operated one of Scotland's largest and most successful deep water harbours for more than 40 years, says that Global does not need to become a harbour authority to fulfill its growth ambitions.

Global counters that thousands more jobs could be secured for the area if the government agrees to the "harbour revision order". It could then compete for offshore work with large yards in Norway, the Netherlands and the north of England.

Global also claims it is well-placed to win a significant amount of new business from two massive offshore wind farms in the outer Moray Firth - the neighbouring Moray Firth and Beatrice offshore wind farms - both of which received planning consent in March 2014.

Global's MacGregor claims to be at a loss as to why the port authority seeks to prevent his company from controlling maritime real estate at the mouth of the Firth. "We are still trying to understand what the port authority's issue is," he said. "We have no interest in interfering with cruise liners. We just want to make our yard as efficient as possible: that would be good for our company but would also be a huge benefit to the economy of the area.

"To run Nigg efficiently we need to be in charge. This is about being able to offer the right services to potential clients in a highly cost-conscious market."

MacGregor also claims that the requested powers would put Global in charge of only one-third of the shipping channel at the mouth of the Cromarty Firth, leaving the port authority with control of the remaining two-thirds of the entrance, amounting to 550 metres. As most cruise liners entering the firth bound for Invergordon are about 30m wide, MacGregor asserts that this should more than meet the needs of the CFPA.

The CFPA replies that the width of the entrance channel is not the issue. Vessels have to keep to the right-hand side of the channel as they go in and out of the firth, so separate exit and entrance channels are needed. In addition, there are certain weather conditions in which large ships, or those tugging oil rigs, would need to pass through what would be Global-controlled waters.

Buskie says the powers Global is pushing for are "not needed" and would effectively hand the company control over all shipping entering and leaving the Cromarty Firth, ­including the right to charge harbour dues, board vessels and pass bylaws. "From a business perspective in terms of their ­engineering, we don't understand why they need to become a port authority in order to continue doing what they do," Buskie said. "Global has in the past ­flourished under our governance model. Our fear is that someone else could inherit these powers.

"This is not about Global Energy against the CFPA: this is about a private company getting control of a public asset. It's the biggest threat to the port since it was created in 1973.

"It would be very wrong if this part of the firth was taken out of public hands and given to a private company that is already 25% owned by a Japanese company. At a time when the Scottish Government is planning to introduce legislation that would allow land in the Highlands to be taken out of private hands and into public ownership, we cannot allow the strategic entrance and exit to the firth to move out of public ownership and into private control."

Buskie claims that, if Global is given the powers it wants, it would effectively amount to a "land grab" whereby a "private company was allowed to privatise a national asset" with taxpayers, stakeholders and the local community getting nothing in return.

This would contrast with the CFPA's custodianship of the firth as a trust port that reinvests surplus profits in the port and the community, as happens at other trust ports in Scotland, including ­Aberdeen, Lerwick and Peterhead.

"If this goes ahead it will endanger jobs at Invergordon as companies operating from Invergordon will be at a ­competitive disadvantage as boats would have to pass through Global's waters to get to Invergordon," Buskie said.

"Vessels entering the Cromarty Firth would have to contact two separate port authorities, obtain consent and arrange pilots all before entering ­Invergordon. They would also incur two sets of harbour dues, rendering Invergordon uncompetitive and leading to the loss of quality jobs."

The CFPA also plays the environmental card, claiming that having two statutory authorities would "add confusion" with potentially disastrous results in the event of a pollution incident such as an oil spill, when quick management decisions are needed.

For Alf Baird, professor of maritime business at Edinburgh Napier ­University, the spat between Global and CFPA vividly demonstrates the need for greater ­competition within Scottish ports.

He points to the Scottish tradition, upheld by both private and public port owners, of opposing competing developments in areas of their control. Instead, he says, they should follow the ­example of ports in continental Europe that lease out terminals to a range of private operators. "This means there is less conflict of interest and more competition within ports," Baird said.

"[Public] Port trusts [like the CFPA] can be just as rapacious as privately owned port authorities, and have been known to operate in the interests of ­trustees, albeit while claiming that surpluses are used for reinvestment."

Baird maintains that port infrastructure in Scotland is "way behind" the large ports of northern continental Europe such as Zeebrugge, Rotterdam and Hamburg, which have become "real engines for economic growth" for the Benelux countries and Germany.

"The UK's port policy of privatisation and light regulation is arguably one of the main reasons for the UK's worsening trade balance," Baird said.

"The UK is simply no longer a competitive place from which to export, and ports are critical when it comes to trade."

With so many vested interests at stake in the Cromarty Forth, can a speedy resolution be found? In ­December, an attempt by the local MSP Rob Gibson to get the two sides in the dispute to reach agreement through the Scottish Arbitration Centre was turned down by Buskie, who said that a negotiated compromise was not appropriate in this dispute as it was a "straight choice between public or private ownership of a hugely important national asset".

Last month Highland Council submitted a formal objection to ­Global's plan but said that it would try to broker an agreement. A 42-day consultation period ended on Boxing Day. All eyes are now on the Scottish Government, which is expected to announce shortly whether it will accept or reject the application, or put it to a public or local inquiry or a hearing. Either way, the storm over northern Scotland's main window on the world is unlikely to blow itself out quickly.