Is the closed season on Jews over? Are English Jews facing rising levels of violence and abuse? Anthony Julius certainly thinks so. The lawyer, best known for representing the late Diana, Princess of Wales in her divorce, but also the author of a book on T S Eliot and anti-Semitism, has written a capacious history of anti-Semitism in England, Trials of the Diaspora, out next week. In it he expresses his "provisional judgement" that the situation facing Anglo-Jewry "is quite bad, and might get worse".

Coincidentally, the report on anti-semitic incidents in 2009 by the Community Security Trust (CST), was published last week. At first view, it makes alarming reading, and seems to confirm Julius's worst fears. CST recorded 924 anti-Semitic incidents in 2009, the highest annual total since it began recording such incidents in 1984, and – after two years of falling numbers – an increase of 69 per cent from 2008.

But peer closely and the picture is more complicated. The main reason for the surge, CST noted, was the unprecedented number of anti-Semitic incidents recorded in January and February 2009, during and after the Israeli invasion of Gaza. Of course, this is no reason to rejoice: if someone is trying to thump you, the fact that they're screaming that it's revenge for what Israel is doing in Gaza isn't going to make you feel a whole lot better. It didn't help that during Israel's 2006 war with Lebanon, the Prime Minister Ehud Olmert said: "I believe that this is a war that is fought by all the Jews." If the Israeli government (wrongly) elides Israel with all Jews, it's hardly surprising if anti-Semites do too.

These days you rarely hear the kind of unthinking middle-class anti-Semitism current in, say, 1961, the year in which An Education, the film based on Lynn Barber's memoir, was set. Philip French, in The Observer, wondered if the real-life counterpart of the headteacher (Emma Thompson), given to sneering rants about the Jews killing Jesus, would have been really so strident. Yet only a few years earlier, a teacher in my primary school declared one week that all Jews were rich, and the next that the Jews killed Jesus. (My Holocaust survivor parents, angry but also anxious, wrote anonymously to the headteacher. By the following week, the teacher was gone.)

If anti-Semitism of this kind seems to have disappeared altogether, we live in postmodern times where some of what looks like anti-Semitism isn't, but, conversely, some of what doesn't look like anti-Semitism in fact is. Consider the "philo-Semitism", for instance, of Michael Gove and Julie Burchill ("the Jews are my favourites"; "Jews do things so well"). Burchill's philo-Semitism is a form of anti-Semitism, I'd suggest, because it bunches all Jews together, as though we were a single, uniform entity. The idea that all Jews are wonderful is little different from all Jews being hateful: in both cases Jews are stripped of individual characteristics, and are nothing except Jewish – a view to which most racists happily subscribe. If Burchill, as is rumoured, converts to Judaism, she'll discover that some Jews are nice and others not – rather like the rest of the human race.

Today racism, it seems, can be ironic. I've heard of campuses where non-Jewish students josh their Jewish friends with comments like: "Stop hoarding the milk, you Jew." Is this too close to the bone, or is it fatally unsatirical to take offence? Some young Jews find it amusing, yet recognise that such playing with stereotypes can only be done between consenting adults – close friends with licence to shock one another.

It is also, they recognise, a dangerous game which, under the guise of playfulness, might also allow the venting of real prejudice. How far is it from Tottenham supporters calling themselves the Yid Army, to Chelsea fans chanting "Spurs are on their way to Auschwitz", as they do when the teams meet? Some non-Jewish Tottenham fans argue that, on the contrary, their happy embrace of the "Yiddo" label is a way of neutralising anti-Semitism.

But there are limits to irony. Last Monday, a new page opened on Facebook, called "Hi, I'm a Jew. I don't care about COD [Call of Duty, a video game mostly played by boys] or Periods, I just want your gold". By Thursday it had 3,040 fans, peddling the hoariest stereotypes of money-grabbing, wealth and noses. Another Facebook page is called "Racist Jokes". This includes such gems – hold on to your hats – as "What's the difference between a pizza and a Jew? A pizza doesn't scream when you put it in the oven", and "What's the difference between a Jew and a boy scout? The boy scout came back from the camp.'

That some of these postings are poorly spelt and written is no reassurance. There's bravado here, of course: teenagers thinking it's cool to be outlandish, following in a long tradition of crudely anti-Semitic jokes charted by Julius. These latest, though, are amplified by the internet's reach and anonymity, which not only allows you to reinvent your own identity but see other people's as equally fictitious.

Those young Jews who have protested have, of course, been accused of lacking a sense of humour (though one young Jew expressed disgust about "Racist Jokes" by commenting: "The person who made it is probs a fucking Paki who needs to go back to their own country"). Yet when a Jewish teenager directly confronted friends who'd signed up to the pages, they apologised and professed themselves ashamed. They'd made no connection between cyber anti-Semitism and the feelings of real, embodied Jews.

Modern anti-Semitism is a complex phenomenon, but Anthony Julius, for all his often thoughtful analysis, ultimately falls back on the elision of anti-Zionism and anti-Semitism, and the notion that the Zionist is the Jew by another name. Perhaps the best way of countering such reductionism is to reverse it: the BNP's Nick Griffin and the Polish MEP Michael Kaminski have shown that neo-Nazi anti-Semitic sentiments and support for Israel are quite compatible.

We should never be complacent about anti-Semitism, but neither should we allow some Jews to exaggerate it, regard it as inevitable, use it to try and delegitimise criticism of Israel or see it as an altogether different kind of animal from other more socially accepted kinds of racism such as Islamophobia. Those who hate are rarely so discriminating.