Your right to marry is subject to national laws on marriage, including those that make marriage illegal between certain types of people (for example, close relatives),

Although the government is able to restrict the right to marry, any restrictions must not be arbitrary and not interfere with the essential principle of the right.

This text is taken directly from the Human Rights Act.

Article 12: Right to marriage

Men and women of marriageable age shall have the right to marry and to found a family, according to national laws governing the exercise of this right. 

Example case - B & L v the United Kingdom [2005]

English law prevented a parent-in-law from marrying their child-in-law unless both had reached the age of 21 and both their respective spouses had died.

B was L’s father-in-law, and they wished to marry. L’s son treated his grandfather, B, as ‘Dad’. The court accepted the Government’s argument that the law had the valid aim of protecting the family and any children of the couple. But it held that their right to marry had been violated. The law was based primarily on tradition, and there was no legal reason why a couple in this situation could not have a relationship. There had also been several cases where couples in the same circumstances had obtained exemptions by personal Acts of Parliament (laws for the benefit of individuals). This showed that the objections to such marriages were not absolute.

(Case summary taken from ‘Human rights, human lives: a guide to the Human Rights Act for public authorities’. Download the publication for more examples and legal case studies that show how human rights work in practice.)