Tens of thousands of people marched through British cities on Saturday to protest against Israel’s ruthless onslaught on Gaza, which has left almost 2,000 civilians dead. Hamas has been firing rockets into Israel, too, causing fear and trauma. I do not think a legitimate sense of grievance can excuse Hamas’s daily strikes.

However, Israeli children, mothers, fathers, grandmothers and grandfathers have not been bodily threatened to anywhere near the same degree by Hamas in the past few weeks. Israel’s actions are gravely disproportionate.

The demo was organised by the Stop the War Coalition – a group which has been active since the illegal war on Iraq, holding power to account. Many conscience-stricken British Jews were there, so too some Hasidim.

Massive marches took place in South Africa, led by the noblest of men, Archbishop Desmond Tutu. I didn’t join the marchers in London because, well, I was worried that I would lay myself open to charges of anti-Semitism. Which is what happened when, some time back, I went out on a march against the Israeli strangulation of Gaza. So, cowardice prevailed over principle this weekend. Not proud.

I do, though, want to examine and understand anti-Semitism in Britain and the West, which may turn out to be even more risky than holding a placard and shouting slogans. A week ago, Channel 4 News tried to persuade me to go and talk about the attacks on synagogues and Jewish people since the beginning of the latest Gaza campaign. I said I couldn’t comment because my thoughts and feelings were in chaos. I could easily condemn obvious anti-Jewish hatred.

The vile abuse, graffiti and attacks across Europe are sickening; ethnic or religious groups should never be collectively blamed and scapegoated, in times of war or peace. I see too many emails and tweets expressing the vilest forms of abuse. Jewish people have been impugned and experienced indescribable horrors throughout their history. Outrage and criticism should be directed at the current, inhumane Israeli government, even if its actions in Gaza are backed by the majority of its people, many of whom are too frightened to know better.

What I couldn’t get my head around, though, was the way extreme and even reasonable Zionists were pointing to anti-Semitism as a way of shutting down debate.

In pictures: 2014 Israel-Gaza protest in London Show all 12 1 /12 In pictures: 2014 Israel-Gaza protest in London In pictures: 2014 Israel-Gaza protest in London Israel-Gaza protest, London Protesters march down Regent Street on 9 August (Getty) Getty In pictures: 2014 Israel-Gaza protest in London Israel-Gaza protest, London A religious Jewish man stands with pro-Palestinian supporters during the rally in Hyde Park on 9 August (Getty) Getty In pictures: 2014 Israel-Gaza protest in London Israel-Gaza protest, London An image tweeted by the Palestine Solidarity Campaign from the 'roof of the BBC' (PSC/Twitter) Palestine Solidarity Campaign/Twitter In pictures: 2014 Israel-Gaza protest in London Israel-Gaza protest, London A protester at the rally in London on 9 August (Getty) Getty In pictures: 2014 Israel-Gaza protest in London Israel-Gaza protest, London People stand with their placards during the London protest on 9 August (Getty) Getty In pictures: 2014 Israel-Gaza protest in London Israel-Gaza protest, London A Gooners Against Apartheid flag during the march on 9 August (Karim Ghani/Facebook) Karim Ghani/Facebook In pictures: 2014 Israel-Gaza protest in London Israel-Gaza protest, London People wave banners from a property in Mayfair as a rally to support the people of Gaza passes by on 9 August (Reuters) Reuters In pictures: 2014 Israel-Gaza protest in London Israel-Gaza protest, London A Spurs Fans Against Apartheid banner on 9 August (Karim Ghani/Facebook) Karim Ghani/Facebook In pictures: 2014 Israel-Gaza protest in London Israel-Gaza protest, London An aerial image tweeted by the Palestine Solidarity Campaign (PSC/Twitter) Palestine Solidarity Campaign/Twitter In pictures: 2014 Israel-Gaza protest in London Israel-Gaza protest, London Demonstrators join a rally to support the people of Gaza in central London on 9 August (Reuters) Reuters In pictures: 2014 Israel-Gaza protest in London Israel-Gaza protest, London A protester clad in the colours of the Palestinian flag joins the rally on 9 August (Reuters) Reuters In pictures: 2014 Israel-Gaza protest in London Israel-Gaza protest, London Protestors listen to speeches in Hyde Park at the end of the march on 9 August (Getty) Getty

False accusations are currently flying around and hurting good people. That is simply unacceptable. The decision of the Tricycle Theatre to drop the Jewish Film Festival because a small amount of funding came from the Israeli government was not proof of left-wing Jew-hatred, as some neocon and Jewish Chronicle journos allege. It must have been a tough call, made in good faith. The theatre’s artistic director, Indhu Rubasingham, is a brilliant artist, not a political animal.

The chair, Jonathan Levy, a good friend, is a man of deep integrity – and is himself Jewish. His wife, Gabrielle Rifkind, is a universally respected expert on conflict resolution – read the recent book The Fog of Peace, which she co-wrote with Giandomenico Picco. I have been to soirées at their home where people on all sides from the various Middle Eastern nations are invited to talk freely.

The theatre took a stand. Those who malign the director and chair say Israel is being picked on. No. If Syria and Isis were funding events at the Tricycle, they might have a point. To claim India, which hosted a film festival there, is as guilty of oppression is absurd. Hundreds weren’t being massacred at the time in India.

The truth is that Israel has historically got away with brutal campaigns in Gaza, but now, with public opinion turning, that deal is off.

False accusations devalue the currency and give deniers real ammunition. Incalculable damage is caused by those who falsely cry rape, racism, Islamophobia, and sexism. Be scrupulous in your response when people are branded anti-Semites – particularly if their accuser is a loyal friend of Israel. Those pointed at may well be anti-Semitic, but they could also be misrepresented.

Exaggerated claims are equally counter-productive. A young American-Jewish journalist who works in Britain castigated the Tricycle and wrote this chilling line: “Watch yourself, Europe. Your roots are showing.” Yes, there have been murders of Jews by Muslim extremists and anti-Semitism is out and about. But she must know that the EU never stops Israel’s killing missions, and that for today’s European fascists the No 1 enemy is Muslims.

Besides clear anti-Semitism and unfair charges of it, there is that most nebulous category: anti-Semitism which could be there or not be, and is impossible to prove or un-prove. An Anglo-Saxon writer said this to me on Thursday: “When babies are being blown apart in Gaza, I can’t get too excited about graffiti about Jews and black flags. There is no comparison. Does that make me anti-Semite?” A reader asked: “They go on about anti-Semitism. What do we call Jewish hatred of Muslims? They don’t let us ask these questions.” Do we brand these people anti-Semites? I really don’t know.

We need to unpick anti-Semitism: its manifestation, meaning and effect. As well as condemning its occurrence, we should name and shame those who fling out the accusation when there is no evidence it is called for.