Skipper Stephen Humphreys, 33, engineer Robert Cameron, 65, and crew member Eric Blackley, 57, perished in freezing conditions when their vessel went down opposite Clydebank’s Queens Quay on December 19, 2007.

The Flying Phantom had been towing the giant 225-metre long Red Jasmine bulk carrier — the largest ship to have visited the River Clyde for around 20 years — before it capsized and sank.

The accident happened as the tug was sailing virtually blind in heavy fog, apart from weak radar signals, with her speed decreasing in relation to the Red Jasmine, which caused the tow rope to slacken.

This led to her ‘girting’ — being pulled over and capsizing.

Last week the High Court in Edinburgh heard of a series of VHF radio messages between the two vessels during which the pilot of the Red Jasmine asked the Flying Phantom to change her position on seven occasions.

The tug later reported that she had ran aground which prompted a message from Red Jasmine for her to ‘let go’ the tow rope, to which the tug responded: “Will do”.

However, it turned out to be her last known transmission as, despite a button being activated to release the tow rope, there was a fatal mechanical delay of up to eight seconds — not previously identified by the tug’s owner Svitzer Marine — before the line would actually disengage.

Advocate Depute, Ms Wade QC, told the court: “Consequently the tug release mechanism did not operate before the tug girted.” Last week Clydeport admitted to failing to have an adequate contingency plan for when fog — frequent in the Clydebank area — is encountered.

It also conceded that it had failed to provide a safety management system and to appoint a suitable people as designated persons.

Following the announcement, Andrew Henderson, from Thompsons Solicitors, which acted for the families of the men who died, last week welcomed the news and urged the Crown Office to begin a Fatal Accident Inquiry into the sinking.

He said: “It is very welcome that today Clydeport have admitted their guilt to a series of health a safety breaches. Almost seven years on from the sinking we have to make sure something like this never happens again.

“The best way to make sure safety on the river is improved is for the Crown Office to begin a Fatal Accident Inquiry into the sinking. There can no more delay on this matter, thousands of men work in the marine industry on the Clyde and the lessons learned from a FAI will help protect their safety in the future.” All three men who lost their lives were members of the Unite trade union and Pat Rafferty, the organisation’s Scottish Secretary, has now called for the Scottish Government intervention to strengthen workplace health and safety legislation.

He added: “By admitting their culpability the law will punish Clydeport with a significant fine but this does nothing for the families of the victims, puts no responsibility on an individual or individuals within the company itself and does nothing to prevent fatalities from recurring in the future.” Flying Phantom owners Svitzer Marine were previously been fined £1.7 million over the tragedy.

On Monday Clydeport was fined £650,000 after Lord Kinclaven said the court required to mark the seriousness of the offending by imposing “a substantial fine” on the harbour authority.

Mr Henderson, of Thompsons Solicitors, said: “This fine imposed on Clydeport shows just how serious the breaches of health and safety regulations were. The sentence sends out a clear message to all companies who operate on the river Clyde that safety must come first.”