Police stood by as the slogan “From the river to the sea” was projected onto Parliament on Wednesday night, a senior Jewish MP has said.

Andrew Percy, a Tory backbencher, raised concerns after pro-Palestinian protesters beamed the slogan onto the Elizabeth Tower, which houses Big Ben.

He spoke out during a Commons debate on Thursday that saw many MPs express fears over their safety and warn that threats from “Islamist extremists” were stifling democracy.

“From the river to the sea” is regarded by many as an anti-Semitic slogan as it implies the eradication of the state of Israel.

Other messages projected onto Parliament by protesters including “Stop bombing Gaza,” “Ceasefire now” and “Stop war now”.

The rally was organised by the Palestine Solidarity Campaign, which has been behind regular marches, including one last Saturday that passed near the Israeli embassy.

It came after Sir Lindsay Hoyle, the Speaker, sparked angry scenes on Wednesday by breaking with convention to select a Labour amendment on Gaza.

He said he had made the decision after being warned of threats to the safety of Labour MPs if they were not allowed to vote on their party’s proposal.

Thousands of pro-Palestinian activists had gathered in Parliament Square, chanting slogans that could be clearly heard in Parliament. Protesters then beamed the slogan “From the river to the sea, Palestine will be free” onto the Elizabeth Tower. 

Mr Percy told the Commons of the rising tide of anti-Semitism, saying: “For months I’ve been standing up here talking about the people on our streets demanding ‘death to Jews’, demanding Jihad, demanding intifadas as the police stand by and allow that to happen,” he said.

“Last night, a genocidal call of ‘From the river to the sea, Palestine will be free’ was projected onto this building. That message says no Jew is welcome in the state of Israel or in that land. This is going to continue happening because we’re not dealing with it.”

Penny Mordaunt, the Commons Leader, told Mr Percy that the authorities were looking into who projected the message and that prosecutions would be brought.

Mr Percy was not the only Tory MP to criticise the Metropolitan Police’s handling of months of pro-Palestinian protests in London, with Matthew Offord, the MP for Hendon, north London, saying: “Many of my constituents have faced a level of anti-Semitism that we’ve never seen before.

“My constituents remind me not only of the calls for jihad on the streets of London and the Metropolitan Police refusing to do anything about it. They also remind me about men driving through north London threatening to rape Jewish women and the CPS [Crown Prosecution Service] then declining to prosecute them.”

Theresa Villiers, the MP for Chipping Barnet, warned that there was “a climate of hardline support which has seen anti-Semitism on the streets of our capital city and my constituents from the Jewish community feeling intimidated about coming into the centre of London”.

Robert Jenrick, a former immigration minister, added: “We have allowed our streets to be dominated by Islamist extremists, and British Jews and others to be too intimidated to walk through central London week after week.

“Now we’re allowing Islamist extremists to intimidate British Members of Parliament. This is wrong. It has to stop.” 

Ms Mordaunt said “British Jews are suffering a grotesque level of hatred and abuse which quite frankly shames our country”.

She added: “There cannot be any tolerance or quarter given to those individuals that threaten and try to prevent MPs conducting their business and honouring the obligations they have to their constituents to use their judgment when they come into this place.”

The debate was triggered after chaotic scenes in the Commons on Wednesday night, which were sparked by the SNP’s bid to force a vote on a Gaza ceasefire.

Sir Lindsay went against the advice of his clerks by selecting a Labour amendment to the SNP’s motion, angering both the Scottish party and the Tories.

He made his decision following intense lobbying from Sir Keir Starmer, the Labour leader, who is said to have told him about the threats Labour MPs were facing. But it sparked a furious response, with SNP and Tory MPs walking out of the chamber en masse at one point in protest.

The Speaker apologised to MPs and denied suggestions he had made the decision to spare Sir Keir the embarrassment of a damaging rebellion, insisting he had been motivated by the safety of Labour MPs.

A Metropolitan Police spokesman said: “This is a chant that has been frequently heard at pro-Palestinian demonstrations for many years and we are very aware of the strength of feeling in relation to it.

“While there are scenarios where chanting or using these words could be unlawful depending on the specific location or context, its use in a wider public protest setting, such as last night, is not a criminal offence.” By Nick Gutteridge, The Telegraph