As the latest activists – two women and a man – threw soup over the two paintings, onlookers could be heard shouting “no” and “don’t do it”.
In a video posted on X by JSO, the activists can be heard telling an angry crowd: “There are people in prison for demanding an end to new oil and gas, something which is now government policy after sustained, disruptive actions, countless headlines and the resulting political pressure.
“Future generations will regard these prisoners of conscience to be on the right side of history.”
A spokesperson for the gallery said three people entered Room 6 of the exhibition just after 14:30 BST and threw a soup-like substance over two works.
The Metropolitan Police said three people had been held on suspicion of causing criminal damage and its inquiries were continuing.
It is the third time in recent years an artwork at the National Gallery has been selected as a target for protest action.
In July 2022, two activists glued themselves to John Constable’s The Hay Wain.