For nearly a century debate has raged over whether he was the man who ignored the plight of hundreds who died in the sinking of the Titanic.

A series of inquiries spanning several decades have failed to condemn or clear Captain Stanley Lord over allegations he turned a blind eye to the "unsinkable" ship's frantic attempts to summon help.

Now a controversial new book has posthumously pointed the finger directly at the mariner - claiming he was a "sociopath" whose callous indifference condemned 1,517 to a watery grave.

What has never been in dispute was that Lord's ship; SS Californian, was in the vicinity of the Titanic when it foundered after hitting an iceberg in the North Atlantic on 15 April, 1912.

The RMS Carpathia, which was almost 60 miles away, steamed to the stricken liner's aid and arrived in America with 723 survivors to a hero's welcome.

In contrast, The Californian, which made her maiden voyage from Dundee in 1902, arrived with none amid claims that it had chosen to ignore the numerous distress flares launched from the Titanic's bows.

Lord subsequently insisted it was far from clear that the vessel, on her maiden voyage from Southampton to New York, was in distress, and so he had been happy to retire to his cabin without taking further action.

The boat's only wireless operator had gone off duty shortly before the Titanic sent her first alarm call.

Now Scottish-American maritime historian Daniel Allen Butler, in his study The Other Side Of The Night has re-examined the evidence and has come to the stark conclusion that Lord, from Bolton, Lancashire, deliberately ignored the doomed vessel's pleas for help.

Butler commissioned a series of clinical psychologists to examine Lord's sworn testimony as well as reports of his actions both before and after the tragedy.

He said their conclusions were unanimous and damning: "It was never contested by Captain Lord, or his officers, that what was seen from the bridge of the Californian were white rockets, which in 1912 were the internationally recognised signal for distress.

"White rockets meant that somebody, somewhere, was about to die, yet Lord choose to ignore them. What has remained unexplained for more than nine decades is why Lord would so callously choose to disregard such a plea for help.

"The answer, which lies in medical science, is that Stanley Lord was a man without conscience: he was a sociopath."

Butler, who lives in California, claimed evidence about the captain's serious shortcoming became clear in the way he reacted to the unfolding tragedy.

There were allegations that he coerced his officers into changing their testimony to match his at "the point of a revolver", while the Californian's log, which would have contained their exact position and mentioned any distress signals sighted, mysteriously disappeared.

"Lord's account of what happened changed dramatically on a number of occasions, while other participants' testimony changed in nothing except minor detail," said Butler.

"Falsifying a log entry is one of the most serious offences which any captain can commit, yet only someone truly credulous would believe that Stanley Lord was not responsible for the alterations and omissions found in the Californian logbook.

"The constantly evolving stories, the reckless disregard for the safety of others and refusal to admit any possibility of wrongdoing are clear indicators of a sociopathic personality.

"In the remaining 50 years of his life Lord never expressed any remorse or regret for his actions or any sympathy for the victims of the Titanic," said Butler.

Lord was never formally charged in connection with the disaster, but was sacked by the Californian's owners.

He died in 1962, still pleading his ignorance of the Titanic's plight and striving to restore his reputation.

Butler has no qualms about delivering what amount to a posthumous guilty verdict on the long dead sailor.

"What Stanley Lord did was morally and legally wrong and that cannot just be ignored because of the passage of time.

"The responsibility of one human being to another is important, and I, for one, am not prepared to forget and let bygones be bygones."

Despite this the author is keen not to claim that the Californian could have saved every passenger.

He said: "In the best case scenario the Californian would have arrived alongside the Titanic no more than ten minutes before it went under.

"In fairness to Captain Lord his ship could have saved 300 or 400 people, but we would have still have been looking at 1,000 people losing their lives."

A 1912 British inquiry into the disaster was critical of Lord for failing to respond to the Titanic distress signals.

However, following a campaign to clear his name, a further probe was launched by the UK Government in 1992.

It too concluded that Lord had "failed to take proper action to respond", but speculated that any rescue effort from the Californian may well have come too late to save large number of passengers.

The report stated: "There are no villains in this story, just human beings with human characteristics."

Lord's defenders insist he was made a scapegoat by Britain's Board of Trade and Titanic's officers, who provided only half the number of lifeboats needed for the 2,240 passengers and crew.

The Other Side Of The Night is published by Casemate.

The 'unsinkable' ship

The Royal Mail Steamer (RMS) Titanic took three years to build at a cost of more than £4 million.

- It was 882ft (269m) in length, 175ft (53m) in height and had a fully loaded weight of 46,328 tons.

- The ship's 29 boilers had a daily consumption of 825 tons of coal.

- Its top speed was 23 knots.

- The ship was so new when passengers boarded it on 10 April, 1912, that the paint was still wet in several areas.

- It was stocked with 40,000 eggs, 75,000 pounds of fresh meat and 1,000 bottles of wine.

- The ship contained a heated swimming pool, a first for any sailing vessel.

- On the fateful maiden voyage 2,240 passengers were on board, 1,517 perished and 723 survived.

- The ship was loaded with only enough lifeboats to hold around half of the Titanic's passenger. There were 20 of them with a total capacity of 1,179.