The writer and journalist Ari Shavit warned on Sunday that Israel was “facing an existential threat” which was much more dangerous than “old threats to its security.” In a coruscating speech, he blamed his own camp of progressive Israelis for failure to address political and social problems so that they were perceived as “detached” from reality and Israeli society.

A leading columnist with Haaretz, who wryly described his job as “to challenge dogmas and to speak inconvenient truths”, Shavit told the paper’s first London conference that “the main challenge facing Israel is threefold. One is the fact that the one-state situation is developing into a cancer that will soon be irreversible. In my mind, we have no more than a decade, perhaps less”.

If settlers continued to rise in numbers in the West Bank, then by 2025 “the Zionist project will be over. We will have passed the point of no return.”

The second challenge facing Israel, said Shavit, was “the attack on its legitimacy. Israel is losing its legitimacy. If Israel becomes a pariah state and the West turns its back on Israel, we have no future. That’s more dangerous to us than all the security problems we face”.

And the third element, he said, “is the attack on Israel’s democracy”. He charged the “new Israeli right”, both religious and secular, of “betraying the Jabotinsky traditions with unprecedented attacks on the democratic values which made Israel so great. First they went after Haaretz; then the ‘lefties’; then the Supreme Court. Now they go after the IDF!”

Occupation, said Shavit, was “much more dangerous for Israel than for the Palestinians,” because of the undermining of Israel’s essential democratic values. This goes against the grain of the Zionist project”.

But as well as attacking the right wing, Shavit said that liberal Zionists had to ask themselves where they had been during this process. “We (the Israeli Left) failed in 1993, 2000, 2005, and so on — but we couldn’t admit it. And peace became associated with what I call the ‘WASP-y’ elite — White Ashkenazi Supporters of Peace. We did not communicate with our own people and peace became associated with prosperous, privileged, Tel Aviv. If we don’t deal with that issue, we cannot win the minds and hearts of many Israelis”.

The peace camp, said Shavit, had degenerated into a “negative ethos, though for good reasons. We became too critical and too judgmental, and we offered nothing positive or inspirational to say. Bill Clinton and Barack Obama did not win elections by being negative. We dwindled into a kind of political impotence. As much as I despise the settlement project, the settlers have become much more politically sophisticated than we are. And while they were doing that, taking over the country, we sat in our shouting corner like some sort of protest movement from the 1970s.”

He offered advice to the peace camp, ranging from Israeli nation-building to reaching out to the young Jews of the diaspora and to the West. “Every Jew in the diaspora has a stake in Israel”, he said. “I don’t want Jews in the diaspora to be shut up. On the contrary. What happens to us affects you, what happens to you affects us. It is totally unacceptable that you will be expected to stand by Israel, whatever happens, and that you will not have a say in where Israel is going.”

And his last injunction – “We must just do. Enough of the protests and the petition writing. It’s time for us to grow up and be leaders in the real world.”