Incidents of antisemitism rose by 11% in the first six months of this year compared with the same period in 2015, according to the Community Security Trust.
The overall figure of 557 cases of malicious acts was the second highest ever recorded during a January-June period, the CST said.
There was no obvious trigger for the increase, said the organization, which provides security to the UK Jewish community. Two years ago, the war in Gaza led to a big rise in antisemitic incidents in the UK.
But the biggest increases this year were recorded in April, May and June, months when antisemitism in the Labour party was the subject of widespread media coverage. Racism and xenophobia were part of the campaign discourse in run-up to the EU referendum on 23 June.