If there's one thing we know about Israel, it is that it doesn't listen to its enemies. Those implacably hostile to the Jewish state can rant and rave, but Israel simply closes its ears. If anything, such criticism only makes the country dig in its heels, confirming its gloomiest, most isolationist instincts: "see, everyone really does hate us ­- all the more reason for us to retreat from the world, becoming the people that dwells alone".

Criticism from its friends, though, is a different story. Then, no matter how reluctantly, Israel is forced to listen. Witness the current relaxation of the blockade on Gaza. That did not come about because pressure from anti-Zionist activists and the Arab world got too much. It happened because, after the flotilla debacle, Israel's number one ally, the United States, declared the blockade "unsustainable". Now some other friends of Israel are speaking up - and they could have an even more profound impact. I am speaking of the Jewish diaspora.

Of course, there have always been Jewish critics of Israel, but they have usually been found on either the strictly-Orthodox or ultra-left margins. Those in the Jewish mainstream have, for decades, been solid in their mostly uncritical support. If they had any misgivings, they kept them to themselves in the name of presenting a united front. Now something is shifting.

The first sign is the success of
J Street, the "pro-Israel, pro-peace" lobby in the US that in little more than three years has acquired more than 100,000 supporters, as well as both credibility and influence. The defining feature of J Street - which has made it impossible to brush aside - is that designation as "pro-Israel". These are not the anti-Zionist usual suspects, but friends of Israel - steeped in their commitment to the country - who are nevertheless calling for a change in course, for Israel's own sake.

Now J Street has found an echo across the Atlantic in the form of JCall, an online petition of European Jews launched in the past few weeks. Note the names of those involved. Early French signatories include the charismatic intellectuals Bernard-Henri Levy and Alain Finkielkraut, two men who have long defended Israel and Zionism and have the scars to prove it. They were joined by two former Israeli ambassadors as well as Britain's own David Hirsh, the indefatigable fighter against the attempted academic boycott of Israel. These are not people who can be written off in the usual fashion, as on the fringe, as anti-Zionists or, heaven forbid, as "self-haters".

The voices are becoming too loud and too numerous

The same is true of Peter Beinart, whose recent essay for The New York Review of Books - titled 'The Failure of the American Jewish Establishment' - has been filling up email in-boxes around the Jewish world. Beinart excoriated American Jewish leaders for blindly endorsing a steady slide away from the liberal values US Jews hold most dear, and warned of the likely result: young American Jews severing their links to Israel altogether. The Aipac crowd have attacked Beinart, insisting that there is only a binary choice - either back Israel always or join its enemies - but they cannot dismiss him: he is a former editor of the ultra-Zionist New Republic magazine.

Now this group of dissenters has a new, even more improbable recruit. Mick Davis, who heads both the UJIA, the largest pro-Israel charity in Britain, and the Jewish Leadership Council, wrote in last week's JC that diaspora Jews had every right to speak out. He binned the usual refrain - that we have no right to criticise because we don't live there - insisting that diaspora Jews are "buffeted by the same winds which assail Israel". He went further, faulting Israel for lacking a strategy to escape the current rut and declaring that the diaspora has a "legitimate role" to play in helping to construct one.

The McCarthyites of the Jewish right will doubtless try to trash Davis and the others - but it won't work. The voices are becoming too loud and too numerous. Their message to Israel is clear: "We love you, but enough is enough." They speak not as Israel's enemies, but as its friends. The question now is, will Israel heed these warnings before it's too late?