The Community Security Trust, which advises Britain's estimated 260,000 Jews on safety, said the surge came as figures showed a significant rise in such incidents for the first six months of the year.
While there was no obvious reason for the general increase, it noted that July's rise took place at the same time as the Israeli offensive against Hams militants, in which it has pulverized the enclave from air, land and sea, killing more than 1,200 men, women and children.
On the Israeli side 53 soldiers and three civilians have been killed.
"There is no excuse for this wave of racist intimidation and violence and we call upon all good people to unequivocally condemn it," said CST spokesman Mark Gardner.
Tens of thousands of Britons have taken part in protests in London and other cities against the Israeli action. Pro-Palestinian activist groups stress that they oppose Israeli government policy and are not hostile to the Jewish people.
Some of the signs at protests have however been distinctly anti-Jewish.
The Trust said there had been 304 anti-Semitic incidents between January and June, a 36% rise compared to the same period a year ago. Since the start of the offensive at the beginning of July, 130 anti-Semitic incidents had been recorded - the second highest month on record.
Although the overall total this year has increased, there were fewer violent assaults recorded, down 32% to 22, and the vast number of incidents related to verbal abuse, graffiti and abuse via social media.
The number of recorded incidents had been falling in recent years from a high in 2009, also sparked by conflict between Israel and Hamas in Gaza, when politicians said that British Jews faced a "real and growing danger."
This month's surge in incidents has also provoked concern.
The Archbishop of Canterbury, spiritual head of the world's 80 million Anglicans, voiced unease at the impact of the conflict in Gaza.
"While it is acceptable to question and even disagree with particular policies of the Israeli government, the spike in violence and abuse against Jewish communities here in the UK is simply unacceptable," he said in a statement.
"We must not allow such hostility to disrupt the good relations we cherish among people of all faiths."
Member of parliament John Mann, chairman of a parliamentary group against anti-Semitism, said the report was troubling.
"From the feedback we are receiving, it is likely that the volume of anti-Semitic incidents will increase significantly before the year's end," he said.
Gardner said the rise in recorded anti-Semitic events this year might reflect better reporting as well as more actual incidents.
Anti-Jewish incidents have also take place in Germany and France in recent weeks, including petrol bomb attacks on synagogues and cultural centers.