By Mark Kinver
Science reporter, BBC News website
New research shows early humans were living in Britain around 700,000 years ago, substantially earlier than had previously been thought.
Researchers are confident the tools are 700,000 years old
Using new dating techniques, scientists found that flint tools unearthed in Pakefield, Suffolk, were 200,000 years older than the previous oldest finds.
Humans were known to have lived in southern Europe 780,000 years ago but it was unclear when they moved north.
The findings have been published in the scientific journal Nature.
A team of researchers from the UK, Italy and Canada found a total of 32 flint tools in a fossil-rich seam at Pakefield. They say it represents the earliest unequivocal evidence of human activity in northern Europe.
One of the team, Chris Stringer of the Natural History Museum's Department of Palaeontology, said the discovery of evidence of early human activity in Britain was startling.
"Until recently I certainly would not have believed that there would have been humans this far back," he said.
Professor Stringer told reporters at a media briefing in central London that the tools displayed all the hallmarks of human workmanship, and were not the result of natural erosion.
"One of the worries is that perhaps things like this can be produced by rocks bashing together in a river bed. These are not in this context, so we are confident that these are stone tools."
The tools were used for scraping, cutting and sawing
The scientists said they were happy that the artefacts were 700,000 years old because there was a range of evidence that all converged on the same age.
One factor was the discovery, at the same location, of teeth from a species of water vole that existed in this period.
Professor Anthony Stuart, from University College London, told reporters this played a key role in dating the site.
"A modern water vole has molar teeth that grow all the time and have no roots. Its ancestor, called Mimomys savini, had rooted teeth which did not grow.
"Nobody in northern Europe has before found any evidence of humans in association with this older water vole."
Until this find, it was thought that humans arrived in northern Europe 500,000 years ago, after archaeologists unearthed a shin bone and two incisor teeth along with a number of flint tools at Boxgrove in southern England.
The earliest evidence of human existence in southern Europe dates back 800,000 years at sites in Spain and Italy.
It was thought that humans did not move to the colder north because they were unable to adapt to factors such as longer winters and shorter growing seasons.
However, Professor Stringer said soil samples from the Pakefield site revealed that the climate 700,000 years ago was similar to the present day Mediterranean region.
"We have learned from Pakefield and its fantastic biological evidence that it was significantly warmer so people could move north without adaptation.
"They also had the same sort of plants and animals to exploit."
The megafauna that would have roamed Europe during this period included rhinoceroses, elephants, sabre-tooth cats and hippopotamuses.
The geography was also very different from the present day. Britain was connected to the continent by a land bridge, which would have allowed early humans to move in and out easily.
The land was low with no steep hills. Very large rivers dominated the landscape and could have been used as tracks by migrating humans.
'Stone Age gold'
The Pakefield site was on the floodplains of the River Bytham, which was Britain's largest river before it was destroyed by glaciers some 450,000 years ago.
Commenting in Nature, Wil Roebroeks of the Netherlands' Leiden University, said the team's data was "Stone Age gold" but it did not provide evidence of colonisation.
"The Pakefield artefacts probably do not testify to a colonisation of the colder temperate environments of northern Europe, but more to a short-lived human expansion of range, in rhythm with climatic oscillations."
Professor Stringer said the discovery opened up a whole new area of research.
"The fact that we know that there were people in Britain at this early date means we can start to look for further evidence of them and perhaps one day be lucky enough to find fossil remains of these people."