Under the law of the United Kingdom, high treason is the crime of disloyalty to the Crown. Offences constituting high treason include plotting the murder of the sovereign; committing adultery with the sovereign's consort, with the sovereign's eldest unmarried daughter, or with the wife of the heir to the throne; levying war against the sovereign and adhering to the sovereign's enemies, giving them aid or comfort; and attempting to undermine the lawfully established line of succession. Several other crimes have historically been categorised as high treason, including counterfeiting money and being a Catholic priest.

Succession to the British throne is determined by descent, sex, legitimacy, and religion. Under common law, the Crown is inherited by a sovereign's children or by a childless sovereign's nearest collateral line. The Bill of Rights 1689 and the Act of Settlement 1701 restrict succession to the throne to the legitimate Protestant descendants of Sophia of Hanover who are in "communion with the Church of England". Spouses of Catholics were disqualified from 1689 until the law was amended in 2015. Protestant descendants of those excluded for being Roman Catholics are eligible.