The water company found the ancient settlement containing historic artefacts while preparing to lay new water pipes to protect the future of Letcombe Brook, near Wantage.
Some of the human skeletons are likely to have been involved in ritual burials, while other finds included evidence of dwellings, animal carcases and items such as pottery, cutting implements and a decorative comb (pictured below).
The items have been carefully removed by the Cotswold Archaeology for forensic examination.
Thames Water will now be able to start laying the six-kilometre pipe which, following consultation with residents, will supply nearby villages with water taken from groundwater boreholes near the River Thames and not Letcombe Brook.
Chris Rochfort, Thames Water environmental manager, said: “We’ve found significant historical items on many previous upgrade projects but this is one of our biggest and most exciting yet.
“This is a £14.5 million project which is going to have real benefits for the environment by reducing the need to take water from the Letcombe Brook, a chalk stream which is a globally rare and highly important habitat for us to protect. As a result, future generations will be able to enjoy it for years to come – and now they can also learn about their village’s secret history.”
In his “jaws of death” headline grabbing speech last month, Sir James Bevan chief executive of the Environment Agency warned that chalk streams – most of which are in England – are “under threat”.
Chalk streams are “geologically vital” and support a rich biodiversity such as trout, voles, otters and kingfishers.
Sir James said: “They are under threat because their aquifers currently provide drinking water for millions in southeast England, and that is unsustainable in the long term.”
The Environment Agency is working with water companies to reduce – or in some cases end – abstraction from chalk streams.
Neil Holbrook, chief executive of Cotswold Archaeology, said: “The new Thames Water pipeline provided us with an opportunity to examine a number of previously unknown archaeological sites.
“The Iron Age site at Childrey Warren was particularly fascinating as it provided a glimpse into the beliefs and superstitions of people living in Oxfordshire before the Roman conquest. Evidence elsewhere suggests that burials in pits might have involved human sacrifice.
“The discovery challenges our perceptions about the past and invites us to try to understand the beliefs of people who lived and died more than 2,000 years ago.”
Within its revised draft £10.9 billion business plan for 2020-25, Thames Water has committed to reducing pressure on rare chalk streams as well as dropping the amount of water taken from water courses with low flows. The brook runs from Letcombe Regis to East Hanney and is home to protected species such as water voles and white-clawed crayfish.
Southern Water uncovered two ancient skeletons during sewer replacement works in Ramsgate, Kent in 2016.