Dr Stephen Sherlock has been investigating a Neolithic site at Streethouse Farm, Loftus, North Yorkshire, since 2016, where he has found the remains of a brine-storage pit, with three associated hearths, and other Neolithic artefacts, buried up to three metres underground.
It's thought that the seawater was concentrated into brine using evaporation at the nearest beach at Skinningrove and was then carried up to the clifftop for further processing by boiling the liquid to create salt crystals.
The Neolithic, says Dr Sherlock, was a time of great change when the Mesolithic hunter-gatherers were being replaced by farmers who stayed in one spot to grow their crops and rear animals.
Keeping male beef cattle alive over winter would need a large amount of fodder, so they would be killed and the meat preserved using salt.
Dr Sherlock said: "There are earlier Neolithic sites particularly in the Balkans, Romania and Poland, where they are manufacturing salt as early as 5000, 5300BC.
"But we are saying this is the earliest find in the UK and Western Europe.
"I believe that they would have done the first stage process on the foreshore to go from seawater to a salt brine concentrate, and then it is transported to the site as a second stage.
"Then it is refined and the final process is that it is boiled down to provide salt crystals."
Dr Sherlock said they excavated through what would have been a Neolithic domestic dwelling, indicated by a series of posts, finding objects including a quern stone, which was used for grinding and a pounder.
Underneath were three areas of intense burning, which he believes were the hearths, surrounded by fire-reddened, wedge-shaped stones, which he believes could have been props for the oven furniture and ceramic vessels containing the brine.
In all 3,000 items have been excavated - all Neolithic, including flint tools and leaf-shaped arrow heads, blades and flakes which are still "razor sharp", and bits of pottery "as big as your hand".
There's still more to find and there's hope they can carry on digging this year - depending on Covid restrictions.
Dr Sherlock, who previously found the earliest beer in Britain in a dig on the A14, said: "We are not at the bottom - in places we are three metres down.
"It's like writing a book, until you get to the end, you don't know who did it. I might be in the last chapter, but not on the last page."
At least 1,000 saltworks have been found dating back to the Iron Age and 31 in the Bronze Age, but until the Street House find, dated to 3,800 - 3,700BC, there has been no known Neolithic sites.