A Glasgow University archaeologist has helped convince the descendants of a soldier killed in the Anglo-Zulu war that he was not the coward they once feared.

Jane Mann, a relative of a casualty of the Battle of Isandlwana in 1879, will take delivery of a specially commissioned painting by military artist Jason Askew at a ceremony in London today.

Ms Mann is the great-great-great grand-niece of Lieutenant Nevill Coghill who, along with his fellow officer Teignmouth Melvill, was killed while attempting to save the 24th Regiment of Foot's colours from capture by Zulu warriors who had earlier annihilated a British column of soldiers.

They were the first soldiers to be awarded the Victoria Cross posthumously.

The regiment had faced around 25,000 Zulu warriors, armed mainly with the traditional iron spears and cow-hide shields, although there were a number of muskets and old rifles. The attack marked the first major engagement of the war.

The 1800 British, colonial and native troops and around 400 civilians were armed with state-of-the-art breech-loading rifles and had two seven-pounder field guns.

The battle was the subject of the 1979 film Zulu Dawn, which starred Peter O'Toole, Burt Lancaster and John Mills.

It was a prequel to Zulu, which was released in 1964 and starred Stanley Baker and Michael Caine. The film depicts the Battle of Rorke's Drift, which took place on the same day as the Isandlwana massacre. Famously, the garrison of 150 British and colonial troops defended against an intense assault by 3000 to 4000 Zulu warriors.

The story of Coghill and Melvill's dash from the Isandlwana battlefield was controversial. Sir Garnet Wolsely, who commanded the latter part of the Zulu campaign, was against them being honoured. He said: "I am sorry that both of these officers were not killed with their men at Isandlwana instead of where they were. I don't like the idea of officers escaping on horseback when their men on foot are killed."

Ms Mann admits she herself questioned her forebear's behaviour on the battlefield.

To uncover the truth she contacted Dr Tony Pollard, director of Glasgow University's Centre for Battlefield Archaeology, who had already undertaken an extensive archaeological investigation of the Isandlwana site.

He and Ms Mann, who studied history at Oxford University before embarking on a career in publishing in the fields of both military history and education, are currently researching the battle for a forthcoming book entitled The Colours of Courage, which examines perceptions of bravery in conflicts throughout history.

Dr Pollard said: "The British Empire suffered a major embarrassment at Isandlwana, which was its heaviest defeat at the hands of indigenous troops. Victoria Crosses weren't awarded till 1907 because it was such a disaster for the army. That's why they awarded 11 for Rorke's Drift, the most awarded for one engagement. It redirected attention from a disaster to a victory."

He said that despite contemporary paintings and etchings in the Illustrated London News showing Melvill and Coghill together fighting to protect the colours, the evidence was that they had left the battlefield separately.

They met up at the Buffalo River and Coghill managed to get across, but Melvill got into trouble.

Dr Pollard continued: "So Coghill goes back to help him and in doing so throws away any chance of getting away. They are overrun by Zulus and die together."

He added: "I think Coghill left to save his own skin. A diary entry recorded he had injured his knee while chasing a hen, but it was known he had suffered a knee injury as a child.

"My feeling is he shouldn't have been on active service in the first place and was a liability. But my conclusion is that he redeems himself at the end going back to save a fellow officer."

Ms Mann will pass the painting to the Victoria Cross Museum where it will assist in promoting the work of the Victoria Cross Trust in renovating the graves of VC recipients.