On Friday after nightfall Jewish communities the world over will be celebrating the spring festival Pesach (Passover) as usual.

Preparations often start as early as January, with every corner of the house or flat cleaned thoroughly from top to bottom. But most people start seriously after the carnival festival of Purim, exactly a month before Pesach. The most in-depth cleaning takes place in the kitchen, with every crevice scoured and special non-leaven foods bought or prepared, and once-a-year crockery and cutlery brought out in honour of the occasion.

But Pesach is not really about food and fun: it is there to teach us a grim story.

Everywhere the Jewish community has lived outside of Israel has been regarded as 'galut', the miserable diaspora existence in which we are not only told by G-d that we are strangers in a strange land, but life teaches us this every minute of the day, every day of the week, every week of the year.

This week demonstrations have been held outside Parliament objecting to antisemitism in the Labour Party led by Jeremy Corbyn. In 2018 Britain, that this should be necessary simply beggars rational belief.

But then Jew-hatred is not and never has been rational. And politics is not the only culprit. For decades we have known that antisemitism is rife in our universities, and yet nothing is done. Justifications from 'freedom of speech' are used when it suits, and only when it is a question of Jew-baiting. No other minority would allow academic institutions to get away with this type of behaviour.

Then there are sermons at Easter or after the latest terrorist attack. Antisemitism has been built into the wording of official church services, especially at Easter, and some Easter hymns I have heard are still shockingly antisemitic in terminology. And as for terrorist attacks, I have actually read and heard more than one Anglican bishop using language that implies a comparison between Isis and 'the Jews'.

So when you have political parties, churches and universities (often aided and abetted by the media) feeding off each other, no wonder we don't have to go back thousands of years to our sojourn in Egypt to remind ourselves of what being a stranger in a strange land is all about. Egypt is here in front of us – every day of our lives.

So what do Pesach and the Seder service around the table teach the Jewish people? How can we find something positive in our daily experience of conflict and crisis? The answer is the concept of 'bitul', which means self-abnegation. This is not self-abasement and silence, but the knowledge that we should be open to G-d's divine mercy.

This time of year, so often in Jewish history fraught with murders and rampage on behalf of the host societies in Europe, hell-bent on celebrating their own spring festival in style (which meant cutting down any Jew who happened to be around, and burning a synagogue or two, not to mention rapes and pillage), reminds us to be both vigilant and open to the divine.

We have to have rules, but we also have to bend them. Around the Seder table we play at not being slaves, but at being the master for the day. We enact the role that we hope will be ours in the Messianic age of controlling our lives in our own land, and not in one which is foreign to us in all but language. And we eat the 'bread of humility' known as matzah, instead of the normal inflated bread made with yeast which rises.

At this time of year par excellence, we know that we are not simply individual Jews, but an entire 'people', an 'am'. In Hebrew 'am' is related to 'with'. We are a people who are with each other in communion and as siblings. We are a tiny people of 14 million, most of whom now live in the State of Israel. In this country we number 250,000, around 0.3 per cent of the total population. And yet, at this time of year, we feel that we are simply one Jewish family – aware that all over the world other families are also celebrating our joint redemption from Egypt to the Promised Land by dint of G-d's grace and mercy.

We know in addition that our tiny religion of Judaism and our tiny people, the Children of Israel, have given hope, love and true belief to the world. It is our prophet Moses who first advocated helping the poor, the lonely and the widow financially, spiritually and psychologically. It is Moses who declared it to be the greatest sin imaginable if anyone starved, and who insisted on giving every member of the household, including servants, one day off free from work, to rest as G-d did in his creation of the world.

It is Moses who told us not just to love our neighbours as ourselves, but to love the stranger. Believe me, loving the stranger, a person who is completely unknown and alien to you, is far more difficult than loving the enemy. The enemy is known and is often admired. But to love the unknown is possible only with 'bitul', with the opening up into the new, the novel, the dangerous and the threatening. And throughout our history, we Jews have learned to do this: we are practised in the art of being both the stranger and also being open to the stranger. The 'enemy' is often a person made in our image who simply doesn't agree with us, whereas the stranger is uncanny, 'unheimlich' in German, and beyond all comprehension.

Without the teachings of Judaism there would also be no concept of justice in the world. The seven Noachide laws incumbent on gentiles include kindness to animals and setting up courts of justice.

Judaism is a live and let-live religion, which only advocates stringent laws for itself and not for others. And yet, for thousands of years, Jews and Judaism have been under attack, libelled, slandered and subject to attempted destruction.

But each year we, the Jewish people, manage to survive and find ourselves here together once again at Pesach time as we sit round the Seder table, telling the story of the Haggadah, of our ancestors in Egypt whom G-d redeemed through miracles, well aware as we speak that history repeats itself in every generation.

And each year at Pesach around the Seder table, we ask G-d once again to redeem us from the Egypt of our present life, as we look ahead to the next festival of Shavuot (Pentecost) which takes place in exactly seven weeks time and celebrates the giving of the G-d's teaching (the Torah) to Moses on the tiny hill known as Mount Sinai.

Only this year it is especially painful and scary to acknowledge that the call of 'Dayenu', the universal Pesach cry against antisemitism, has for the first time in history been heard outside London's Parliament Square.

Yes, in the streets of London, we, the Jewish community, have just before Pesach expressed what we have known for a very long time – England is no longer the home of the free, Blake's promised 'green and pleasant land.'

No, England has now become the new dry and dessicated land of Egypt, a country where churches, universities, politicians and educationalists think it is OK to demonise us Jews such that we now feel it necessary, once again in our history, to cry out to G-d, finally 'enough is enough.'

So when we finish our annual Seder meal round the table on Friday night with the cry 'Next year in Jerusalem', we will know as never before that there is only one Jerusalem: the one in Israel – our true home.

Dr Irene Lancaster is a Jewish academic, author and translator who has established university courses on Jewish history, Jewish studies and the Hebrew Bible.