The UK's Official Secrets Act of 1989 entered into force on March 1, 1990. As the UK government explains in this guide,
"The 1989 Act replaces section 2 of the Official Secrets Act 1911, under which it was a criminal offence to disclose any official information without lawful authority. Under the 1989 Act it is an offence to disclose official information only in six specified categories and only if the disclosure is damaging to the national interest."
The 1989 Act, below, has secondary legislation and amendments.