The excavations at the site in the Medway Valley uncovered the items in deep sediments believed to come from the Ice Age some 300,000 years ago.

Around 800 stone artefacts were dug up by researchers from University College London, buried in enough material to fill a sinkhole and ancient river channel.

Two big flint knives, believed to be hand-axes - and chipped on both sides to produce a symmetrical shape - were among the artefacts.

The tools would usually be held in the hand and were used to butcher animals and cut meat, experts believe.

Those found at the site have a distinctive shape, a long and finely worked tip, and a thicker base.

Senior archaeologist Letty Ingrey, from the UCL Institute of Archaeology, said: "We describe these tools as 'giants' when they are over 22cm long, and we have two in this size range.

"The biggest, a colossal 29.5cm in length, is one of the longest ever found in Britain.

"Giant hand axes like this are usually found in the Thames and Medway regions and date from over 300,000 years ago.

"These hand axes are so big it's difficult to imagine how they could have been easily held and used.

"Perhaps they fulfilled a less practical or more symbolic function than other tools, a clear demonstration of strength and skill.

"While right now, we aren't sure why such large tools were being made, or which species of early human were making them, this site offers a chance to answer these exciting questions."

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Further discoveries

The site is thought to be dated in the early prehistory of the UK, when Neanderthal people were beginning to emerge, possibly alongside other human-like species, and would have likely been a wild landscape of wooded hills and river valleys.

The team also found a Roman cemetery at the site, likely to be around 250,000 years older than the Ice Age artefacts, with the remains of around 25 individuals discovered, possibly from a nearby Roman villa.

Nine of the buried bodies were discovered with personal items such as bracelets, and four were found in wooden coffins.

The digs were commissioned ahead of the development of the Maritime Academy School in Frindsbury, and the findings have been published in the Internet Archaeology journal.