Pro-Palestinian protesters were seen carrying “extreme anti-Semitic” signs comparing Gaza to Auschwitz and Benjamin Netanyahu to Hitler at a demonstration in London on Saturday.

Another placard showed a snake in the colours of the Israeli flag wrapped around the globe, an anti-Semitic conspiracy theory about Jewish control.

The signs were spotted hours after Boris Johnson, the former prime minister, warned in a video posted on X, formerly known as Twitter, of a “spectre of anti-Semitism” that was “on the rise on the European continent”.

A spokesman for the Campaign Against Anti-Semitism said: “If the people at these marches are all intent on peace, why are they content to walk alongside such extreme anti-Semitic images and chants without calling them out?

“Grotesquely likening Gaza to Auschwitz, or Benjamin Netanyahu to Adolf Hitler, abhorrently attempts to state that the Israeli government is somehow comparable to the Nazis.

“Such vile rhetoric diminishes the impact of the Holocaust – the genocide of six million innocent Jewish men, women and children – and shows contempt for its victims.”

Chants of “From the river to the sea” were also heard from some protesters. Suella Braverman has said the chant had become a “staple of anti-Semitic discord” and was “widely understood as a demand for the destruction of Israel”.

The Campaign Against Anti-Semitism spokesman said: “It has also been well-established by this point that the slogan ‘From the river to the sea, Palestine will be free’ is a genocidal call for the destruction of the world’s only Jewish state.

“As we commemorate those who gave their lives to fighting anti-Semitic evil, one has to wonder what they would make of some of the people on our streets today.”

The Telegraph has approached the Palestine Solidarity Campaign for a comment.