His death was the stuff of legend: stabbed in the back as he valiantly tried to stop his men from firing on the islanders of Hawaii.

But for 225 years, it seems, our perceptions of the glorious demise of Marton-born Captain James Cook may owe more to 18th century spin than reality.

A previously unrecorded watercolour was unveiled today which focuses renewed attention on the long-disputed final moments of the navigator and explorer whose dangerous voyages to exotic places received universal acclamation.

It depicts Cook not nobly protecting life, but in hand to hand combat, fighting with natives after going ashore at Kealakekua Bay on February 14, 1779, to investigate the theft of one of his boats by an islander.

The unedited picture was painted by Deptford artist John Cleveley from first-hand accounts made by his brother James, who was a carpenter on the Resolution during Cook's third, fateful voyage.

The watercolour was among a collection which formed the models for a famous set of aquatints, the work of engraver Francis Jukes and published by Thomas Martyn in 1788.

Advertised as "scarcely to be distinguished from the original Drawings", the prints followed John Cleveley's work closely...with the remarkable exception of Cook's death.

The artist's depiction of Cook fighting for his life on the beach in the left foreground has been replaced by the dramatic moment of his death. The substituted version shows Cook, not in hand to hand combat, but turned away from his assailants, signalling to his ships to cease fire while an Hawaiian chief prepares to stab the navigator in the back of the neck.

This glorified image of Cook as noble hero was famously depicted in John Webber's drawing Death of Captain Cook, first engraved in 1782, and subsequently in a painting by Francesco Bartolozzi and William Byrne.

This would have called on the eagerly-accepted but disputed claim of a Lieut.

King who recorded: "...the Captn called to them to cease fyring and come in with the boats intending to embark as fast as Possible, this humanity perhaps proved fatal to him...he had got close to the Sea side when a chief gave him a stab in the Neck or Shoulder, with an iron spike, by which he fell."

King also reported: "While he faced the natives, none of them had offered him any violence but, having turned about to give his orders to the boats, he was stabbed in the back and fell with his face in the water."

By the time Martyn published the plates in 1788, John Cleveley had been dead for two years and this may have become the "authorised" version of Cook's death, showing him as dying heroically, a victim of his humanity.

"It was, perhaps, enough, to persuade him to alter Cleveley's representation, "said Christie's specialist Nicholas Lambourn at yesterday's unveiling. "With the artist dead, one assumes the engraver was charged to alter the scene."

The set of four original Cleveley watercolours, which have passed down through the family of Quaker philanthropist Ann Hopkins Smith, of Olney, Buckinghamshire, who died in 1851, are expected to fetch up to GBP 150, 000 when auctioned at Christie's in London on September 23.

The exact chain of event's surrounding Cook's death are still hotly debated but scholars have concluded that he acted with uncharacteristic rashness and provocation to the islanders of Hawaii. He was also betrayed by panic and inefficiency among the armed marines whose job it was to protect him.

Cook's horrified officers concocted an account which made a scapegoat of only one man, a Lieutenant Rickinson. But Captain William Bligh, who was famously to lose his ship, Bounty, to mutineers in ten years later, was present at Kealakekua Bay and later damned the account as "a most infamous lie" and "a pretty Old Woman story".

In Bligh's opinion, the main cause of the tragedy lay with the marines, who, after firing a first a first panicked volley when the party became outnumbered by an angry crowd of natives, fell back in fear to their waiting boat.

Bligh blamed the marines' commander, Lieutenant Molesworth Phillips - "a person who never was of any real service the whole Voyage, or did anything but eat and Sleep."

Cook himself, however, whose life - and death - have been immortalised in accounts, elegies, pictures and plays, must shoulder part of the blame. A brilliant navigator, seaman and man-manager, he displayed a previously-unseen cruelty on his last voyage, administering dozens of floggings to his men and exacting barbaric revenge on islanders who stole from his ship.

At the same sale, a pocket hammer carried by Capt. Cook should fetch up to GBP 30, 000. The rare personal relic was presented to his friend and patron, Sir George Jackson, second secretary to the Admiralty, judge advocate of the Fleet and for whom Cook named Port Jackson - modern-day Sydney Harbour.

*In his three voyages of discovery, Cook did more than any other navigator to add to our knowledge of the Pacific and the Southern Ocean.