It was the political equivalent of running into a burning building with a can of petrol and liberally chucking the fuel over anything you could find.

What Jeremy Corbyn did this morning almost defied belief. Even in these extraordinary times, it was an act of such reckless abandon that veteran political correspondents watched open-mouthed.

Mr Corbyn came to the launch of his party’s report into antisemitism, conducted by Shami Chakrabarti, after the worst week of his decades-long political career.

And he left the press conference at Savoy Place, in central London, in an even more dire position than he entered it.

Given the events of the last few days, you might ask how things could get any worse for Mr Corbyn? But there it was, played out in front of our eyes: a Jewish Labour MP baited until she fled the room, targeted with the baseless accusation that she had colluded with a national newspaper; BBC and national newspaper journalists booed for asking about the party’s floundering leadership.

At the head of it all, the leader himself, appearing to compare the democratic state of Israel to terrorists. In the room it sounded as though he made a direct likeness to “Islamic State”.

It was not even a careless throw-away remark – he had written it in advance and included it in his prepared speech. That text suggested he had said “Islamic states”. Either way, the damage was done.

Jewish Labour activists grimaced as the recommendations of the report – mainly sensible and outlining a half-decent way forward for the party to tackle Jew haters in its ranks – were not only overshadowed, but blown away by the man who launched the inquiry in the first place.

Ms Chakrabarti had herself admitted it was “not a report that will keep you up late”. At barely 30 pages long she was right, but what happened later will give many people sleepless nights.

Mr Corbyn’s lack of action as Ruth Smeeth ran from the room prompted one Labour MP to later describe the leader as “a f***ing disgrace”. A veteran Jewish activist said the morning had been “a Shami shambles”. Even if she is rewarded with a role as a Labour candidate at the next election, Ms Chakrabarti – calm, sincere and measured - must rue getting involved.

John Mann, chair of the All-Party Parliamentary Group Against Antisemitism and the Labour MP who challenged Ken Livingstone, said Mr Corbyn had been “clumsy” in his use of language, adding “but he never was a wordsmith”.

It was not over. Even as Mr Corbyn and Ms Chakrabarti left, Mark Wadsworth, the Momentum activist who had challenged Ms Smeeth, set about verbally abusing Luke Akehurst, a pro-Israel party member who is hoping to play a role on Labour’s National Executive Committee.

When he was done with Mr Akehurst, Mr Wadsworth cornered a Daily Telegraph reporter and harassed her until the chairman of the Commons’ press gallery intervened to restore calm. In the background, other journalists gasped as news of Boris Johnson’s decision not to stand for the Conservative leadership broke. What a week.

The signs were there from the start. When we arrived at the venue, my colleague Rosa Doherty was asked by one Labour member: “Do you know what this event is? I’ve turned up to support Jeremy. I’ve heard Jeremy is Jewish. Not that I mind or anything, but is he?”

Mr Corbyn had pleaded with his colleagues to set the “gold standard” for anti-racism in politics. How hollow his words sounded as chaos erupted around him.

We may never know how the hard-left pro-Corbyn Momentum activists came to be at the launch. Were they invited?
By the party, or by the leader’s office? How else would they have known the time and location?

Outside the Westminster bubble such details are irrelevant. Labour stands on the edge of a precipice. Its relationship with British Jews is so deeply damaged that it may never be repaired.

The only comparable experience I have had covering political events was at a BNP rally on College Green in which Nick Griffin had eggs thrown at him. It is to this level that one of the great parties of British politics has now sunk.

Mr Corbyn smiled as he said he was enduring “torrid days”, before adding that his ambition for a “kinder, gentler politics” was “still a work in progress”.

On today’s evidence, such hopes are pure fantasy, both for him and for all of us.