Just Stop Oil protesters have been arrested after smashing the glass covering a Diego Velázquez painting at the National Gallery in London, as police detained dozens of others who blocked Whitehall.

Two activists targeted the glass on the Rokeby Venus painting with safety hammers before they were arrested on suspicion of criminal damage.

The artwork, which was painted by Velázquez in the 1600s, was slashed by the suffragette Mary Richardson in 1914. One of those involved on Monday said: “Women did not get the vote by voting; it is time for deeds not words.”

The Metropolitan police said at least 40 activists who were “slow marching” in Whitehall were also detained and that the road was clear after traffic was stopped for a brief period.