We are currently in the exciting final stages of preparation for our autumn exhibition at the Jewish Museum, and there is an uneasy sense that the history we are telling is still echoing around us.

Our next subject is "blood". This hugely important substance is the focus of so many key Jewish rituals and is also a potent metaphor for identity. We have used it to define ourselves and our practices but have also been defined by it.

We are drawing together a huge and fascinating range of materials, from manuscripts to movies, to explain how blood can unite and divide. And a key part of this will be an examination of the blood libel.

I never thought I'd see a British politician forced to denounce publicly a Medieval antisemitic slur, but Jeremy Corbyn's team has recently declared in the JC that ''Jeremy wholly rejects and condemns the blood libel against the Jewish people''. How can an ancient racist myth about Jews consuming Christian blood still be causing trouble today?

Blood is the vital life-giving fluid that we have in common. It also carries profound significance in Jewish ritual and belief. The word appears in the Hebrew Bible over 350 times. In the Exodus story it is the first plague, and the pascal lamb's blood is smeared on the doorpost to save Israelites. At the giving of the Torah on Mount Sinai, Moses anoints the Israelites with the blood of a sacrificial bull.

Blood is at the heart of traditions such as circumcision, menstrual purity, and kashrut, all central to Jewish identity.

But while the potent metaphor of blood unites Jews as a people, it also divides Jews from other peoples. Christianity introduced the idea of the blood sacrifice through Jesus, in striking contrast to early Jewish thought in which atonement came through sacrificial animal blood and human life is held to be sacred. In Medieval Europe the extraordinary significance given to the blood of Jesus led to a series of false allegations towards Jews, who were believed to have shed the blood of Jesus, both at circumcision and crucifixion. The myth grew that Jews ritually murdered Christian children to use their blood during the festival of Passover. Some of the most notorious blood libel cases originated in Britain.

The first recorded ritual murder allegation was in Norwich in 1144. Following the death of a boy called William, the recently established local Jewish community was blamed, despite there being no evidence. William was martyred and a cult around him grew, spreading across Europe. We will display a 1493 document from Nuremberg, which shows how the myth lingered.

In Lincoln the 13th century blood libel of Little Saint Hugh drew pilgrims for centuries and was referenced in Chaucer's Canterbury Tales. In 1955 the Anglican Church put a plaque at the site of Hugh's former shrine in Lincoln Cathedral, asking forgiveness for Jewish lives lost owing to blood libels throughout Europe. We will be playing audio recordings of English folk ballads immortalising Hugh.

The blood libel myth persisted for centuries, and travelled far, reaching the Middle East via Christian missionaries. In the ''Damascus Affair'' of 1840, where local Jews were accused of the ritual murder of an Italian monk, there was international condemnation, not least British. Sir Moses Montefiore personally intervened to secure their release, and following intense debate on its letters pages, The Times published an English translation of the Passover service to disprove the ongoing claim that Jews used Christian blood at Passover.

We will be showing a copy from our collections of a blood libel edition of Speakers' Notes: Antisemitic Lies Exposed, which was produced in the 1930s by the Board of Deputies of British Jews to combat rising anti-Semitism from groups such as the British Union of Fascists. The level of historical and theological detail of the document is a telling reminder of the persistence of the blood libel for political ends.

On the surface, this choice of subject may seem a world away from our current Judith Kerr retrospective. However, Kerr's flight from Nazi Germany to London can be traced to the Nuremberg Laws, which defined individuals by ''bloodline''.

The chilling blood libel ''special edition'' of Der Sturmer that we will have on display shows familiar medieval myths circulating in modern Europe.

The blood libellers believed that Jewish blood and Christian blood are essentially different. However, the progress of medicine and technology challenged this notion. By the Second World War advances in medicine and technology meant it was possible to safely store, transport and transfuse human blood. In a 1944 appeal for blood donors which will feature in the exhibition, a wounded US soldier is shown with a drip next to the caption "Whose blood will save him? Protestant, Catholic, Jew…It's all AMERICAN blood!" Once one person's blood could flow through another's veins, the idea that humans should be defined through their blood started to change.

Genetic science has since demonstrated that genes, rather than blood, provide the mechanism through which heredity is passed. You might imagine that the potency of blood as a metaphor for identity could not survive this scientific scrutiny, and that a slur like the blood libel would become powerless.

But blood remains very powerful indeed in our imaginations. It is complex. It persists as both a symbol of the creation of a people in a covenant with God, and a symbol of universal humanity.

While it also continues to exist as a symbol of racial myths, we cannot simply consign the blood libel to history, but we can - we must - continue to interrogate its appearances, past and present.

The writer is chief executive of the Jewish Museum. 'Blood' will open on November 5.

www.jewishmuseum.org.uk