The origins of the unique Anglo-American legal system are said to lie in a mix of Anglo-Saxon customs, norms and laws, and some Roman law imported from the continent for good measure. Its original point of development is said to have occurred sometime in the 11th-13th centuries, particularly with the Magna Carta (1215), and the enactment of the Assize of Clarendon (1166) promulgated by Henry II, which transformed English law and laid the bedrock for a system we continue to maintain and develop today not only in the Anglosphere but also much of the commonwealth, such as India and Pakistan.
If we adopt a euro-centric legal history, then it becomes obvious that English law has no parallels. However, if we begin to expand the scope of enquiry beyond Europe’s immediate shores, we may begin to find unsettling evidence of the influence of Islamic law, i.e. shar’ia, on the development of English law. This has long been disregarded both in academia and contemporary debates around the place of Islamic lawin modern Britain. The view tends to be that it is a totally alien construct that has no basis in British society.
However, there is extensive evidence of cross-cultural legal exchange between the Muslim world and post-Norman England that may prove that Islamic law is far closer than we think. The Norman brothers Robert Guiscard and Roger de Hauteville were busy conquering Muslim Sicily in the 1060s, while their Norman kinsman William the Conqueror conquered England in 1066. Roger would come to rule a large Muslim population, who continued to dominate the arts and trade, and Arabic remained the language of administration and literature for a full century afterwards. Statesmen, soldiers and travellers regularly moved between Norman England and Sicily.
England would also be the main contributor to the first, second and third crusades, spanning a period between the 1090s-1180s. The demands created by the crusade’s various needs resulted in innovative legal and financial instruments concerning property, inheritance, debt and other issues to do with the absence of large numbers of men across the seas, and the need to manage and distribute their estates. Like Islamic medicine, Islamic instruments of finance and law came to be adopted and diffused across Europe, but primarily in England.
Therefore, this period was one of in which there was a massive rise in the movement of ideas, goods and even people between the Christian and Muslim worlds. If we consider the influence that Arabo-Islamic civilisation had on European culture via these contact points, this should not come as a surprise. Cross-cultural exchange is the norm, not the exception in human civilisation. This runs contrary to the Whig narrative of history, which considers “medieval” civilisation to have been exceptionally myopic and isolated. However, the human impulse to explore and share is primordial.
John Makdisi, Emeritus Professor of Law at St. Thomas University, has written extensively on this cross-cultural legal exchange. Earlier on, I made the contention that English law was made up of a patchwork of influences. Makdisi, however, believes that there was the dominating influence of a single pre-existing legal tradition that helped to inform the original design of the common law, and that this influence was Islamic law. I generally disagree with monocausal explanations for civilisation-scale phenomena, but his thesis is compelling and contains a great deal of evidence for some sort of formative influence of Islamic law on English law.
The evidence Makdisi cites in his argument is that the legal reforms of 11-13th century England contained revolutionary concepts that were totally out of character with existing European legal institutions. This included: (1) contract law permitting the transfer of property ownership on the sole basis of offer and acceptance, (2) property law protecting possession as a form of ownership in cases of dispossession, (3) trial by jury. These principles had no parallel in continental Europe, but they did further afield: in the Muslim world, in the ‘aqd, istihqaq, and lafif, respectively.
The concept of a contract that permitted the transfer of property ownership at the time of the formation of the contract (before delivery) was a novel introduction to England by the royal courts. It radically diverged from the local and ecclesiastical courts, nor did it have any relation to contract formation in continental Europe. It was Islamic law in which there was a clear parallel to this. The ‘aqd shared these principles, and it was around for centuries prior to Henry II’s introduction of this principle to English law.
The assize of novel disseisin was created by Henry II to redress lands unlawfully seized by providing a speedy means of establishing rightful possession. In essence, it protected ownership by protecting possession itself as evidence of ownership. The process by which this was undertaken included the forming of a twelve-member jury that would inspect the property and the facts of the case and declare these facts to the court, who would then determine whether the plaintiff had been ‘disseised’ unjustly from his property.
This had no prior in either Anglo-Saxon or Roman law. Yet, it bears a stunning similarity to istihqaq as formulated in Islamic law, whereby a plaintiff who had his property unjustly seized also had to prove possession, and a jury of twelve witnesses were also called upon to declare the facts to the court. If the plaintiff could prove his possession prior to its usurpation, then the usurper had to prove that they had more of a right to the property.
The prevalence of trial by jury is perhaps the most distinctive aspect of the Anglo-American tradition, and one of the holdouts of the common law under threat by the expansion of the administrative state and its civil code ethos. Heralded as the “palladium of our liberties”, it gave people the right to be judged not by impersonal laws or superstitious ordeals, but by their own peers who knew them. This meant that a twelve-member jury from the locality had to provide a unanimous verdict on a matter they had seen or heard, and this was binding on a judge.
This is the exact same concept found in the lafif, a Maliki-formulated legal principle. It was Malikism that dominated in Muslim North Africa, Spain and Sicily, the primary points of contact and exchange with Europe. Twelve locals had to look over the facts, swear to tell the truth and have to give a unanimous answer, which was binding on the judge. Of note is that this differs from the Hanafi school of Islamic jurisprudence, lending further credence to the idea that it was contact with Maliki Sicily that led to its introduction to England.
This was the legal system present in Sicily at the time of the Norman conquests, and its diffusion into England would not be a far-fetched conspiracy. It may not be surprising that one of Henry II’s principal advisors, the officer of the exchequer, was one Thomas Brown who had worked in the Norman administration of Sicily, which had largely continued using the Islamic governmental and legal systems laid there by its previous Muslim rulers, including the ‘aqd, istihqaq and lafif.
Although there is a myriad of claims over what influenced Henry II to enact the Assize of Clarendon and the subsequent introduction of the principles Makdisi discusses, what is clear is that the similarities between English law and Islamic law are too close to be dismissed, especially that they share key principles that neither Anglo-Saxon nor Roman law had developed. Their introduction at the peak of Anglo-Islamic contact in the medieval period (the 11-13th centuries) is also no coincidence.
Other academics have written on the cross-cultural legal exchange between England and Islamic civilisation. For example, George Makdisi (John’s father) wrote on the parallels between Islamic and western legal education, such as college, the scholastic community and its method, the license to teach, and the four inns of court and their similarities to the four main schools of Islamic jurisprudence, all having their roots in Islamic civilisation.
As mentioned earlier, some of the most significant developments in English law occurred in the 11th-13th centuries, during the zenith of Anglo-Islamic contact and exchange. The English charitable trust, which bears less resemblance to its European neighbours, instead shares an extraordinary resemblance to the Islamic Waqf, created sometime in the 9th century. Henry Cattan, a Palestinian Christian jurist, wrote generally about English trust and its possible derivation from the Waqf law of Islam.
To establish a Waqf, it had to be in perpetuity, it had to be irrevocable, so that once established it could never be undone, and it had to be inalienable, unless it was exchanged for property of equal value or if the original property had fallen into ruin.A waqf also had to have three elements: a trustee, a qadi, a clearly-defined beneficiary, and a clearly-defined property. This is akin to the four certainties required to establish a trust in English law: certainty of intention, a clear founder, a clear object (the beneficiary), and a clear subject matter (i.e. the trust property).
One such institution that demonstrates the influence of the Waqf on quintessential English institutions was the creation of Merton College, Oxford sometime in the 1260s. Its founder, Walter de Merton, had extensive connections to the Knights Templar, having conducted his business transactions and banking at the New Temple, which is one of the inns of court today, now known as Inner Temple. Claudia Gaudiosi has written a legal analysis of the trust established by de Merton, comparing it with a Waqf deed with which it shares remarkable similarities. 
What John Makdisi has attempted is a unified theory of the English common law as a whole having its origins in of Islamic law. While his thesis of a dominating influence of a single pre-existing legal tradition is interesting, it may not necessarily be true. What is self-evident is that, at the very least, Islamic law has served to be one of the formative influences on English law in a piece-meal fashion and helped to form the characteristics of England’s distinct legal system that defines the Anglo-American tradition against the world.
This relationship should not be dismissed out of hand. While Anglo-American society is notoriously individualistic compared to the countries that most Muslims come from, the formative principles of its legal system are principles that Muslims, too, hold dear and would fight to defend. This provides an opportunity, not just for dialogue, but for collaboration in the defence of our shared legal system and the liberties it provides. Instead of working to try and tear it down, we should reach deep down into our shared traditions to reform and restore our common law.
As a reminder to my readers, all PDFs are located on my e-library (here). Each title below is hyperlinked, leading to a PDF that can be manually located in the Anglo-Islam folder of the e-library. Peruse at your pleasure, and feel free to share all resources here.
 Against Patrick Deneen (II) https://scholars-stage.blogspot.com/2020/06/against-patrick-deneen-ii.html
 Financing Kindness as a Society: The Rise & Fall of Islamic Philanthropic Institutions (Waqfs) https://yaqeeninstitute.org/khalil-abdurrashid/financing-kindness-as-a-society-the-rise-fall-of-islamic-philanthropic-institutions-waqfs/
 Reviving the Waqf Tradition: Moral Imagination and the Structural Causes of Poverty https://yaqeeninstitute.org/zarakhan/reviving-the-waqf-tradition-moral-imagination-and-the-structural-causes-of-poverty/
This is the seminal paper on the relationship between Islamic and English law, which hasn’t received the attention it deserves, nor young scholars who are interested in providing further compelling scholarship such as Makdisi has done.
For some additional reading on the matter of Islamic civilisation's influence on English culture, laws and institutions, this paper comes highly recommended.
This is a good paper to learn more about the practical endeavour undertaken to establish Merton College, and how its trust mirrors much of the Islamic waqf.
The Evolutions and Origins of Islamic Law, Wael Hallaq
This book provides a compelling and intelligible read for those who are not familiar with Islamic law and its history.