It was already known as perhaps the bleakest episode in British history.
Now, new research suggests the Black Death was even more lethal than was previously thought.
The findings go further to exonerate rats as being responsible for the outbreak, which swept the country in the middle of the fourteenth century, killing vast swathes of the population.
Instead, the study claims the disease was passed directly from human to human and was, in fact, pneumonic plague – a more virulent and infectious form than bubonic plague, which has historically been blamed.
As well as spreading more swiftly, the pneumonic variant also killed faster, although – mercifully – it may have been a less painful death.
The new research is to be put forward in a new documentary, Secret History: Return of the Black Death, which also tells the story of a mass burial site in central London, recently discovered by engineers working on the Crossrail project, which involves 26 miles of tunnelling being dug beneath the capital.
Twenty five corpses were found in a small area excavated close to Smithfield Market, last March, buried in neat rows, on two levels, each level sealed below a layer of clay.
They are thought to represent just a tiny fraction of the thousands of bodies which chroniclers at the time described being interred at an emergency burial facility created there by Edward III’s officials in 1348, as the Black Death reached British shores.
Of samples from 12 bodies which were sent for analysis, four tested positive for the deadly bacterium Yersinia pestis, although it is thought they were all victims.
The same bacteria – which is almost identical to the strain still found on four continents – is responsible for both bubonic and pneumonic plague, but the experts taking part in the show concluded that the latter, which is spread by the fleas of infected rats, would not have been able to have the devastating impact caused by the Black Death.
Dr Tim Brooks, an expert in infectious diseases from Public Health England who is based at Porton Down – the Wiltshire site used by the government for dealing with biological threats – said: “As an explanation, for the Black Death in its own right, it is simply not good enough. It cannot spread fast enough from one household to the next, to cause the huge number of cases that we saw during the Black Death epidemics.”
Instead, he identified what he considers was a mutation from the bubonic plague, borne on rats, to the pneumonic variant, whereby it spread to the lungs of sufferers, who then passed it on to others, by coughing.
The incubation period for the latter variant can be as little as a day and many victims would have been dead within 24 hours. The survival rates are far lower than for bubonic plague.
Dr Brooks added: “In a small number of people, before they die, the organism will spread to their lungs and they will then develop a pneumonia. It is that critical switch, that if there were enough people in contact with them, that allows it to spread as a pneumonic plague.”
The theory is supported by separate research showing there are relatively few rat bones from the period and that at the time the disease took hold – December 1349 – it was the depths of winter, when the animals are at their least active.
Don Walker, from the Museum of London Archaeology, who was also involved in the research suggested that the pneumonic form may have killed faster, and did not lead to the growth of agonising boils, or buboes,
“The pneumonic version was more lethal. There was no chance of recovery. You could argue they died quicker and in less pain,” he added.
Mr Walker also oversaw further research, commissioned by Crossrail, to find out more about the victims who were discovered. Of the bodies recovered, 13 were male and three female, while two were children. In the other cases, it was impossible to determine whether they were male of female.
Not all were Londoners. Of ten analysed, six were from the capital. One was thought to be from the south east, two from eastern or central England and one from further north, possibly Scotland.
The team were able to establish such level of detail - including the likely geographical origin - through analysis of the bones, which they can compare with "isotopic signatures" which differ between those of different regions.
The burial site was for those from the city’s poorer classes, with evidence of malnutrition, rickets and anaemia detected – factors which could have contributed to the spread of the disease, making the victims more vulnerable.
The bodies also displayed signs of heavy, manual labour, while one showed evidence of having switched diet, becoming a vegetarian. The team suspect he might have become a monk.
Some of the dead had lived through the initial arrival of the Black Death – in 1348-49 – only to die during later outbreaks. Some of these victims also show signs on violence on their bodies, providing further evidence that the initial outbreak had led to a breakdown of society and period of lawlessness.
Wood Cut Dance of Death Black Death London England 1347-1350 (Alamy)
Total estimates for those buried at Smithfield range from around 5,000 to 50,000 and it has been claimed that bodies would have been carried in at a rate of around one every five minutes.
Ground-penetrating radar analysis, carried out for the programme, to be broadcast on Channel 4 next Sunday, suggests they were carefully buried according to Christian ritual and that great care was taken of the dead despite the scale of the horror.
The programme also features research from Dr Barney Sloane, an archaeologist, who has studied wills from the period to establish that as many as 60 per cent of London’s population at the time – around 60,000 – were killed, in the course of just nine months. This is higher than previous estimates, which have suggested it killed between a third and a half of the populace.
Worldwide, the epidemic is reckoned to have claimed 75 million lives, among them Edward III’s own daughter, Joan, who had sailed to the continent to marry Pedro, heir to the throne of Castile. She she died of the plague within 10 days of landing.
Jay Carver, lead archaeologist on the Crossrail project, said: “We’ve been pursuing all lines of evidence, and we’re really starting to get a great picture now of the detail surrounding what we found and its historical significance, that’s allowing us to solve a 660 year old mystery.”