The Home Secretary has said more must be done to wipe out anti-Semitism in Britain.
Speaking at an event to commemorate Jewish people who died in the Paris terror attacks, Theresa May said "Britain would not be Britain" without Jews, Muslims, Sikhs, Hindus, Christians and people of other faiths.
She added she "never thought I would see the day when members of the Jewish community in the United Kingdom would say they were fearful" of staying in this country.
Her comments come after police lobbied to strengthen the protection of Britain's police officers and Jewish communities after the attacks in France.
Metropolitan Police Assistant Commissioner Mark Rowley has said there is "heightened concern" over the threat to Jewish people - with "continuing anti-Semitic rhetoric" from extremists.
Ms May said: "The dreadful events in Paris are a reminder of the serious terrorist threat that we face.
"The attack on a Jewish supermarket where four people were killed is a chilling reminder of anti-Semitism, not just in France but the recent anti-Semitic prejudice that we sadly have seen in this country.
"I know that many Jewish people in this country are feeling vulnerable and fearful and you're saying that you're anxious for your families, for your children and yourselves."
Speaking on Sky News' Murnaghan programme, former Chief Rabbi Lord Sacks said Jews in Britain were scared to go the shops in the wake of the Paris attacks.
"After what happened in Paris you are beginning to get British Jews asking 'will I be safe going to synagogue or going to a Jewish shop?'" he said.
"Will my children be safe in a Jewish school? And that kind of thing is absolutely inevitable. I hope it will dissipate soon but there can be no doubt that there is an anxiety now among British Jews which is pretty much at a record high within my lifetime."
Four Jewish men were killed at a kosher supermarket in Paris on the third day of the terror attacks in France.
In the wake of the violence, the rabbi of Paris' biggest synagogue told Sky News he believes thousands of Jews will flee France.
Describing it as a "big exodus," Moshe Sebbag, from the Grand Synagogue in the French capital, said: "It's a fact, you can't ignore it."
Ms May said that with "large numbers of Jewish people" emigrating from Europe and others "questioning their future," she wanted to reassure Jewish people they were "an important and integral part" of the UK.
