by Tim Dieppe, Christian Concern
Introduction
Cousin marriage was banned in Britain for a thousand years until the time of King Henry VIII. Then King Henry VIII famously broke with Rome in order to marry Anne Boleyn. Later, in 1540, Henry married Catherine Howard, his fifth wife, who was a first cousin of his second wife Anne Boleyn. To do so, he had to change the law, since marrying such a relative was prohibited and considered incest – even though Catherine was not a blood relative of Henry’s.
The law allowing cousin marriage has remained in place in the UK ever since. The Church of England has a table of Kindred and Affinity which shows all the relations which are prohibited for marriage. Cousins are not listed, meaning that cousin marriage is allowed.
Last year Richard Holden MP proposed a bill to prohibit marriage of first cousins. The bill was presented in parliament in December 2024 when he gave a speech on the issue. Iqbal Mohamed MP opposed the bill, noting the popularity of cousin marriage in some cultures and suggesting genetic testing of prospective couples instead. The issue of cousin marriage was also debated in Parliament in June 2025 in a Westminster Hall debate also proposed by Richard Holden.
The Church banned cousin marriage before
We are so influenced by what the law is where we live and grow up that we often don’t appreciate that it hasn’t always been this way. Joseph Henrich, in his influential book: The Weirdest People in the World (Penguin, 2020), argues that the Church’s insistence on monogamous marriage and the banning of cousin marriages was absolutely crucial to the success of the West. The acronym WEIRD stands for Western, Educated, Industrialised, Rich and Democratic. Without such laws on marriage, the West would not have built such successful societies. His argument is compelling and has been well received.
An appendix to the book lists dozens of rulings against cousin marriage by the Church. For example, the Synod of Trullo in 692 AD formally forbade marriage to first cousins and corresponding affinal kin. In 741 AD, Emperor Leo III made it illegal to marry second cousins, and later second cousins once removed. The Synod of London in 1075 banned marriages up to sixth cousins, including affinal kin. Several other councils reinforced this ruling. This forced people to look outside their families or clans to find partners, with huge benefits for society.