Early humans were living in a balmy Britain 200,000 years earlier than previously thought, say researchers who discovered a set of flint tools.

Humans are known to have been present in southern Europe about 780,000 years ago. Scientists theorized humans did not journey across the Alps into northern Europe until half a million years ago.

Anthony Stuart of University College London and his colleagues discovered 32 black flint tools in river sediments in Pakefield in eastern England. Some of the flakes are more than 20 millimetres long.

Researchers worked at low tide to excavate eroding coastal cliffs in Suffolk to find the artefacts.

The tools were dated to 700,000 years, and include waste flakes chipped away by humans, the researchers report in Thursday's issue of the journal Nature.

At the time, Britain was connected to continental Europe. A range of plant and insect fossils were found at the site that could not survive deep cold.

Based on the species found, the site would have been balmy, the team concluded.

"Parfitt and his colleagues have struck Stone Age gold," wrote Wil Roebroeks, an archaeologist at the University of Leiden, in a Nature commentary.

"Along with hippos, rhinos and elephants, early humans were evidently roaming the banks of these rivers. They did so during a warm interglacial period, and much earlier than hitherto thought for this part of Europe."

It's not known if the early humans used the flint tools to kill animals or scavenge carcasses left by predators. It is "useless to speculate on the technological capabilities" of the tool makers, Roebroeks agreed.

The artifacts and climate evidence suggests the pioneers expanded temporarily into northern Europe when it was warm enough, rather than colonizing the region, the scientists said.