Archaeologists working on the route of the upgraded A14 are trying to work out how our ancient ancestors used toxic plants as food.

MOLA Headland archaeobotanist Lara Carretero Gonzalez at work. Picture: MOLA Headland InfrastructureMOLA Headland archaeobotanist Lara Carretero Gonzalez at work. Picture: MOLA Headland Infrastructure

They found traces of the pulses grass pea and vetch during their work on the £1.5billion road scheme, which covers 21 miles between Huntingdon and Cambridge.

The plants were more often used as fodder for animals - but were also be used for human consumption, especially during times of food shortages, despite their toxicity, which was unlikely to prove fatal but could leave people with head and stomach aches.

Archaeobotanist Lara Gonzalez Carretero, part of the MOLA Headland archaeology team working on the A14, said: "We don't really know what they did because we do not have the direct evidence."

She said the toxins were in the outer coat of the seed which could be removed or washed out to remove the harmful substances - or that the seeds could be simply mixed with other foodstuffs to reduce their effect.

"We are aware they may have washed or soaked the seeds to get the toxins out and they may have boiled them which would have been quicker," she said.

Lara said her Spanish grandmother still washed pulses, although it was unnecessary, because it was the tradition.

Now the archaeologists will use the next phase of analysing the project to try to discover the culinary uses of the pulses in addition to their role as fodder.

Investigation of the toxic pulses comes after the archaeologists found a range of archaeobotanical remains from prehistory through to the post-medieval periods along the route of the A14.

They found staples like wheat and barley at ancient settlements and sites, together with the earliest traces of the beer-making process, and clues on the use of other plants, such as the discovery of seeds from the grass pea and vetch dating back to the Iron Age, came up in the post-excavation process.

MOLA Headland said the seeds had been disregarded as food in modern times because of the bitter taste from the high concentration of toxins in their seed coats, meaning they needed soaking, boiling or removing the coats by hand.

The seeds have also been discovered at sites in the Near East and Europe but it was not known if people were aware of their toxicity. By Roman times, Pliny the Elder was suggesting that the pulses be mixed with cereals to make them more fit for human consumption.

MOLA said little was known about how the pulses would have been cooked in Iron Age and Roman Cambridgeshire.

Thousands of historic artefacts have been discovered by archaeologists working on the A14.