POGS,
The attack on Jeremy Corbyn pre-dated the Oxford Union Labour Club Chair's allegations of anti-semiticism, which came to a head in February 2016. In September 2015 Jonathan Arkush made demands of Corbyn, two of which Corbyn supported. One of the demands was to support Jewish faith schools, which Corbyn refused. At the time, a number of Jewish faith schools were 'failed' by Ofsted for not teaching British values or preparing pupils for life in Britain. Many of the pupils hardly speak English and learn little more than studying the Torah. Many of the schools are illegal and one was ordered to close immediately. You will probably recall that this happened to a number of Muslim schools in the so-called Trojan Horse scandal.
There are a number of articles in the Jewish Chronicle about Corbyn's refusal and there were suggestions he was antisemitic. Corbyn has rebutted the claims in various media, but little of it, including the closure and failing of Jewish schools, made the mainstream media. Very shortly after that, Lord Levy issued the Labour Party with a warning. Again it didn't make the mainstream media.
This all happened in late 2015, since when a number of historic allegations and non-specific smears have emerged. Apparently (so I've heard) there have been tensions in the Oxford Union Labour Club for some time between more liberal Jews, who criticise Israel and tend to sympathise with Palestinians, and more hard line Jews, who claim that any criticism of Israel and support for Palestinians is antisemitic. The Co-Chair's resignation and Lord Levy's threat to withdraw funding from the Labour Party were the culmination of that. I have read suggestions, although I don't know how true they are, that the two groups in Oxford split roughly into Blairites and Corbynites.
I have no idea if this is an orchestrated conspiracy, but it certainly looks as though some people with very passionate views have agendas and other people are jumping on the bandwagon, maybe for their own purposes. Whoever is behind the smears and for whatever reason, it isn't a simple case of antisemiticism being 'rife' in the Labour Party. It didn't just start with Oxford University.