Prohibited degrees of relationship for marriage
You cannot marry certain close relatives, including parents, children, siblings, grandparents and grandchildren, whether the relationship is by blood or through adoption or marriage. Some relationships by marriage, such as a former parent-in-law, can marry in limited circumstances if both parties are over 21 and certain other conditions are met.
Who you cannot marry
The prohibited degrees cover direct blood relatives such as parents, grandparents, children and grandchildren, and siblings including half-siblings, along with equivalent relationships created by adoption.
Relationships by marriage
Certain relationships created through marriage rather than blood — such as a former step-parent or parent-in-law — are restricted rather than automatically banned, and can be permitted where both people are over 21 and the younger party was not treated as a child of the family by the other before turning 18.
Registrars will check
Your notice appointment includes a check on your relationship to each other where relevant. If there is any doubt, be upfront with the registrar rather than risk your notice being rejected close to your ceremony date.
What this means for you
- If a relationship-by-marriage exception might apply to you, raise it with your register office early, as it can require extra evidence.
- These rules exist regardless of consent between the two people — consent does not remove a prohibited relationship.
Official sources
Last reviewed: 17 August 2026 · Next review due 17 November 2026
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Simply Married is an independent planning service, not a register office or government department. Confirm current requirements and fees with your own register office and on GOV.UK.