The operator of a tug boat which sank, claiming the lives of three crewmen, has been fined £1.7 million.

The Flying Phantom capsized in thick fog in December 2007 while towing a cargo vessel on the River Clyde near Glasgow.

At the High Court in Glasgow last month, Svitzer Marine Limited admitted a series of health and safety breaches.

It emerged that the Danish firm failed to act after a similar incident involving The Flying Phantom in December 2000.

Svitzer was fined £1.7 million at the High Court in Edinburgh today.

The sinking occurred six days before Christmas when the tug ran aground in the darkness and fog, and was pulled over on its side by cargo boat the Red Jasmine.

Captain Stephen Humphreys, 33, and Eric Blackley, 57, both from Gourock, Inverclyde, died along with Bob Cameron, 65, from Houston, Renfrewshire.

A fourth man, Brian Aitchison, 37, from Coldingham in the Borders, managed to swim free and cling to a buoy and was rescued.

Port operator Clydeport Operations Limited is also being prosecuted over the incident. A hearing involving the firm will take place in Edinburgh next month.

Judge Lord Turnbull said the case was marked by Svitzer's "enduring failure to take proper account of the level of risk" of towing in reduced visibility, as reported by the company's own experts following an investigation into an incident on the Clyde seven years previously.

On December 29, 2000, the Greenock-based tug suffered £150,000-worth of damage when it was hit by a vessel it was towing, an Egyptian carrier named Abu Eglia.

Company managers identified a high risk of "girting", or the tug being overtaken by the vessel being towed, while operating on a narrow stretch of water in foggy conditions.

Despite this Svitzer did not amend its operation manual or introduce procedures to avert the risk, Lord Turnbull said.

He acknowledged that a financial penalty "might seem entirely inadequate" for the loss of three lives.

The men, he said, "had loving families who have had to endure the grief of their loss over the years until now".

The judge said he found it difficult to understand why proceedings had taken so long to come to court, but said Svitzer had complied with prosecutors throughout the process and that he accepted that the company was "genuinely remorseful" over the tragedy.

On the night of the sinking, the last radio contact with the Flying Phantom occurred just before 6pm when the crew told the Red Jasmine pilot: "We're stuck at present on the bank.''

The court was told the pilot replied: "Let go the line then, please''; to which the Phantom responded: "Will do.''

Mr Aitchison and Mr Humphreys were in the wheelhouse and the others below when the tug lurched to one side.

The survivor pressed the tow release button but "the winch appears not to have released the towline quickly enough", prosecutors said.

Advocate depute Alex Prentice told last month's hearing: "As it started to sink, (Mr Aitchison) was standing on the hull shouting for help, but not being answered.

"As the water started to rise ... he decided to swim for it. He held onto the buoy, shouting for help.''

At 6.15pm, two Clydebank community wardens on the bank heard cries for help and called 999.

One of the men took a boat out on to the river to investigate and found Mr Aitchison clinging to a buoy.

Poor weather conditions meant the bodies of the three other crew were not recovered by divers until December 23.

The Flying Phantom was salvaged the following month.

Svitzer pleaded guilty under the Health and Safety at Work Act 1974 to failing to ensure the safety of its employees.

The company admitted failure to put in place a procedure for instructing employees what to do to avoid the increased risks associated with towing in conditions of darkness and dense fog.

The court heard Svitzer earned a profit after tax of around £2.7 million in 2009.

Skipper Mr Humphreys left behind a wife, a young daughter and two step-sons and was a "much loved son, brother and uncle'', the judge was told at a previous hearing.

In a statement released through her solicitor Mr Humphreys' wife Helen said "I welcome the fact that sentence has been passed on Svitzer Marine Limited today and recognise that the company have admitted their guilt.

"It is a cause of great distress to my family that Clydeport continue to plead not guilty which means more lengthy legal procedures which we have to endure."

Mr Cameron, an engineer, was a father of three daughters and a grandfather. He spent his whole career on the Clyde and was described as a ''well-known, popular character''.

Mr Blackley had been married for 36 years and had a son and a daughter.

His wife remembers him as someone who was always happy and had time to spare for those who needed it, the court heard.

Unite has now called on the Scottish Government to help strengthen workplace health and safety regulations following the High Court decision.

Unite Scottish Secretary Pat Rafferty said: "By the letter of the law justice was served on Svitzer Marine for their role in the preventable deaths of three crewmen but today's judgement reinforces our view that the law is not working for the people it should serve to protect.

"Lord Turnbull said himself that he felt restricted by statute in that he could only impose a fine, noting that it does nothing to help the families of the deceased. 

"It is scandalous they have had to wait six long years for this outcome yet no Fatal Accident Inquiry has taken place, no individual within Svitzer Marine will bear any responsibility for its safety failings and any findings from this process that could improve workplace safety and prevent future fatalities cannot be legally enforced.

"We need to radically change the Fatal Accident Inquiry (FAI) process - something the Scottish Government can do now by fast-tracking the FAI reform proposals made by Patricia Ferguson MSP - and Corporate Manslaughter legislation should be strengthened to ensure that culpability for workplace fatalities is placed on individual directors within the negligent company itself.

"This will be of little comfort to the families devastated by the Phantom tragedy but given that workplace fatalities in Scotland have increased in the last year it's clear we need more robust laws to protect working people."