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Can you marry your cousin
in the UK?

Yes. First-cousin marriage is legal in England, Wales, Scotland and Northern Ireland. MPs have put forward bills to ban it, but none had become law as of November 2026. Here's what the law says, who you can and can't marry, where the debate stands, and what the genetics actually show.

By the DontMarryYourBro team · Updated November 2026 · 7 min read · How we fact-check

The short answer

  • Legal across the UK: first cousins, second cousins and cousins once removed can all marry.
  • Not allowed: parents, children, grandparents, grandchildren, brothers and sisters (including half-siblings), aunts, uncles, nieces and nephews.
  • The debate: private members' bills to ban first-cousin marriage were introduced in 2024–26. None had passed as of November 2026.
  • The health picture: for first cousins, the chance of a serious birth anomaly roughly doubles, from about 3% to about 6%. Most children are healthy.

What the law says

In England and Wales, the Marriage Act 1949 lists the relatives you can't marry, known as the "prohibited degrees." Cousins aren't on the list, so cousin marriage is legal. Scotland and Northern Ireland have their own laws with very similar lists, and they allow cousins to marry too.

Who can you marry in the UK?

For England and Wales:

RelationshipCan you marry?
First cousin (including double first cousins)Yes
Second cousin, or a cousin once removedYes
Step-brother or step-sisterYes. You're not related by blood
Adoptive brother or sisterYes. Adoption only bars marrying your adoptive parent (and your birth relatives)
Your ex's brother or sisterYes
Your ex's parent or childYes, since 2007
Step-parent or step-childOnly if you're both 21 or over and the younger one never lived in the older one's household as a child of the family before 18
Uncle and niece, aunt and nephew (including half-blood)No
Brother or sister, including half-siblingsNo
Parent, child, grandparent or grandchildNo

Not sure exactly how you're related? The cousin calculator names any relationship.

Is the UK banning cousin marriage?

Not so far. In December 2024, Conservative MP Richard Holden introduced the Marriage (Prohibited Degrees of Relationship) Bill to ban first-cousin marriage, mainly on health grounds, and other MPs have backed similar bills. Private members' bills rarely become law without government support, and as of November 2026 cousin marriage remained legal. The debate flares up regularly, so check Parliament's bill pages for the latest.

The arguments on both sides are serious. Supporters of a ban point to the higher rate of genetic conditions and to concerns about pressure on young people. Critics, including some geneticists, argue a ban would target particular communities and that genetic screening and counselling are more effective. We don't take a side on the law. We think every couple, related or not, deserves to know what they carry.

How common is cousin marriage in the UK?

It's most common in some British Pakistani and Bangladeshi families, and in parts of other communities. The best data comes from the Born in Bradford study: 37% of babies of Pakistani heritage born in Bradford in 2007–11 had parents who were first cousins. By 2016–19, the share of Pakistani-heritage mothers there married to a first cousin had fallen from about 39% to 27%.

What the genetics show

  • Born in Bradford (The Lancet, 2013): marriage between relatives roughly doubled the risk of a congenital anomaly, from about 3% to about 6%, after accounting for deprivation.
  • The same study estimated about 31% of anomalies in babies of Pakistani heritage were linked to consanguinity. It found a similar rise in risk for White British mothers over 34.
  • Risk adds up over generations. Where cousin marriage has repeated in a family, even couples who think of themselves as distant relatives can carry first-cousin-level risk.

The risk comes from recessive conditions: cousins are more likely to carry the same hidden gene variant from a shared grandparent. The full numbers.

What cousin couples in the UK can do

  • Ask your GP about a referral to NHS clinical genetics if there's a known condition in either family, or you've lost a baby or child to an unexplained illness.
  • Get a carrier screen together. The NHS doesn't offer broad carrier screening to everyone, but private expanded screens test both partners for hundreds of recessive conditions. Guidelines suggest it for couples who are second cousins or closer.
  • Check thalassaemia and sickle cell if your families come from South Asia, Africa, the Caribbean, the Middle East or the Mediterranean. The NHS offers this in pregnancy; you can also ask your GP before. Thalassaemia trait in the UK.
  • Not sure how related you are? If your families have married each other more than once, a DNA relatedness check measures how much DNA you actually share.

General information, not legal or medical advice. For your situation, speak to a solicitor or your GP.

Sources

  1. Marriage Act 1949, Schedule 1: kindred and affinity (legislation.gov.uk)
  2. Hansard / Parallel Parliament: Marriage (Prohibited Degrees of Relationship) Bill 2024–26
  3. PET BioNews: Bill introduced to ban cousin marriage
  4. The Conversation: Banning first cousin marriage would be eugenic and ineffective (expert view)
  5. Sheridan E et al. Risk factors for congenital anomaly in a multiethnic birth cohort (Born in Bradford). The Lancet (2013)
  6. Risk of birth defects from cousin marriage revealed by Bradford study (PET BioNews)
  7. Small N et al. Changes in consanguineous marriage in Born in Bradford cohorts. Wellcome Open Research (2024)
  8. Bennett RL et al. Genetic counseling and screening of consanguineous couples and their offspring (NSGC). J Genet Couns (2002)
  9. Bittles AH, Black ML. Consanguinity, human evolution, and complex diseases. PNAS (2010)

Cousins? Get your own answer.

A couples carrier check shows whether you two actually share a condition, instead of guessing from averages. Request it from anywhere in the UK.

Request a carrier check

Questions people ask.

Is it legal to marry your cousin in the UK?

Yes. First-cousin marriage is legal in England, Wales, Scotland and Northern Ireland. Cousins are not among the relatives listed in the Marriage Act 1949 or the Scottish and Northern Irish equivalents.

Is the UK banning cousin marriage?

Not so far. MPs introduced private members' bills to ban first-cousin marriage in 2024–26, but as of November 2026 none had become law.

Who can you not marry in the UK?

Your parent, child, grandparent, grandchild, brother or sister (including half-siblings), aunt, uncle, niece or nephew. Step-parents and step-children can marry only in limited circumstances.

Can you marry your step-sister in the UK?

Yes. Step-siblings are not related by blood and are not within the prohibited degrees.

Can you marry your adopted sister in the UK?

Yes. Adoption bars marriage between an adopted child and their adoptive parent, and with their birth relatives, but not between adoptive siblings.

What are the risks of cousin marriage?

For first cousins, the chance of a serious birth anomaly roughly doubles, from about 3% to about 6%. A carrier screen shows whether a couple actually shares a condition.