Supporters of the law – which made extramarital affairs punishable by up to two years in jail – argued that it promoted monogamy and kept families intact. However, seven members of a nine-judge panel at the constitutional court said it infringed on personal freedom.

Constitutional court justice Seo Ki-seok, reading an opinion which represented five of the justices, said: “The law is unconstitutional as it infringes people’s right to make their own decisions on sex and secrecy and freedom of their private life, violating the principle banning excessive enforcement under the constitution.”

Shares in Unidus Corp, which makes latex products including condoms, swelled to the 15 per cent daily gain limit following the ruling.

The controversial law was enacted in 1953 to protect women in a male-dominated society where divorce was rare. The court upheld the law in 2008, but critics claimed that it was outdated in a society where rapid modernisation has often clashed with traditional values.

Around 53,000 South Koreans have been indicted on adultery charges since 1985, but it is rare for people to be jailed. Prosecutors say almost 900 people were charged last year, but none was put behind bars.