A 21-year-old protester who allegedly defaced the iconic Stonehenge site has broken their silence about why they chose to target the beloved prehistoric site.

Just Stop Oil activists Niamh Lynch, a student from Oxford, and Rajan Naidu, 73, a social justice campaigner, allegedly sprayed powdered orange paint on the standing stones about midday on Wednesday (local time).

The act left long orange streak marks across some of the stones of the prehistoric megalithic structure on the eve of the summer solstice celebrations.

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About 8000 people gathered at Stonehenge to mark the longest day of the year in 2023, with similar numbers expected on Thursday for this year’s solstice.

The paint is believed to be made of “orange cornflower”, which will wash away with rain.

In a clip posted to Just Stop Oil’s X account, Lynch explained why Stonehenge was the target of their latest demonstration.

“For thousands of years, people have come to Stonehenge on the solstice to celebrate the beauty of our natural world. But I can’t help thinking, what does it look like today and what the heck have we done to it. These stones have stood here for 5000 years. What will the world look like in 5000 years’ time?” Lynch said.

“It’s time for us to think about what our civilisation will leave behind – what is our legacy?

“Standing inert for generations works well for stones – not climate policy.”

English Heritage, the charity that manages Stonehenge, condemned the attack on X: “This is extremely upsetting, and our curators are investigating the extent of the damage.”

The UNESCO World Heritage Site, one of the UK’s most visited tourist spots, holds spiritual significance and attracts thousands of revellers, spiritualists, and tourists during the summer solstice — the longest day of the year in the northern hemisphere.

However the monument remained open after the incident.

“Just Stop Oil are a disgrace,” Prime Minister Rishi Sunak said on X of the protest.

“The damage done to Stonehenge is outrageous,” opposition Labour leader Keir Starmer said on his X account.

Members of the public were able to walk around within the stone circle, located in southern England, until 1977 when it was fenced off due to concerns over damage from a sharp rise in the number of visitors.

Just Stop Oil has gained prominence in the UK for disruptive environmental protests, with its activists shutting down major roads, disrupting cultural and sporting events and even throwing soup at a Van Gogh painting.

The group wants the UK government to end the extraction and burning of oil, gas, and coal by 2030.

— With AAP