Anti-semitism is known as “the oldest hatred” for good reason.

For 2,000 years, Jewish people have been the targets of hatred, prejudice and discrimination in different parts of the world, in different types of society and for different reasons.

It is rooted in fear of the unknown and hostility to those perceived as “outsiders.”

But in the case of anti-semitism, this has been given a genocidal twist by the ideological conviction that Jews are the enemies of Christianity, nationhood, racial purity, socialism or — today — the oppressed people of Palestine.

These and other vile calumnies have been used by the power-hungry and the deluded to identify a convenient scapegoat, deceiving the ignorant and downtrodden to the benefit of a particular leader or movement.

Home Secretary Theresa May was right to declare that Britain must redouble its efforts to wipe out anti-semitism in her address at yesterday’s service to commemorate the four people recently murdered at a kosher supermarket in Paris.

Her urgent call for more protection for Jewish cemeteries, synagogues and other targets of anti-semitism, alongside greater efforts to combat it through education and on the internet, stands in sharp contrast to government complacency hitherto.

As late as December 29 last year, the Department for Communities and Local Government was trumpeting that its own report “highlights the great strides that Britain has made in fighting anti-semitism.”

Since then, however, a YouGov opinion poll and a survey commissioned by the Campaign Against Anti-semitism have revealed that anti-Jewish prejudice remains widespread among the general population while a substantial minority of Britain’s Jews fear for their future here.

The questions for Theresa May, Local Government Minister Eric Pickles and their colleagues must now therefore be: what additional resources are this Tory-led government prepared to plough into the police, broadcasting and education services to turn fine words into buttered parsnips?

In order to step up the drive against anti-semitism it will also be important to foster unity between all those forces that can potentially be mobilised in support.

Churches have a special responsibility to disown those in their ranks — sometimes in the past at the highest level — who have poisoned the minds of Christians against Jews and Muslims.

Politicians and parties which profess patriotism must take every opportunity to make clear that their notion of nationality is inclusive, not least by highlighting the disproportionately positive contribution that Jewish citizens have made to social, economic, cultural and democratic progress in Britain and its component nations.

Trade unions and the left — much of which has a proud record of combating anti-semitism here and overseas in the 20th century — must continue to expose the pernicious myths that most Jews are especially greedy and wealthy, are bad employers or engaged in some Jewish-led global banking conspiracy.

That, as Engels echoed more than a century ago, is the “socialism of fools.”

There also needs to be sharper clarity as to what constitutes anti-semitism and what does not.

Attacking, criticising or making special demands on people because they are Jewish is anti-semitism.

Attacking or criticising Jewish people or institutions in the sincere belief that they are wrong is not.

Condemning Israeli state policies, or the actions of Israeli governments, is not in itself anti-semitic.

At the same time, Jewish sensitivities about the conditions in which Israel was founded should be understood and appreciated.

Many Jews around the world support the human and national rights of the Palestinian people.

The fight against anti-semitism should not become the pretext for denying those rights.

The struggle for justice and democracy against oppression and dictatorship is indivisible. That, too, must be remembered on Holocaust Memorial Day on January 27.