Thatcher was desperate to stop publication of Spycatcher, by ex-MI5 officer Peter Wright

The government tried to stop its publication

The most explosive claims had already been revealed in Their Trade is Treachery, by Harry Chapman Pincher, published five years earlier, with Peter Wright as its main - anonymous - source.

(The book publicised, for the first time, the allegation that Sir Roger Hollis — a former Director General of MI5 — had been a Soviet spy)

But it was the notion that an MI5 officer could publish a detailed memoir under his own name which alarmed the prime minister. Mrs Thatcher and her advisors believed this would set a dangerous precedent.

After the Security Services Act, the government publicly acknowledged the Secret Intelligence Service [SIS] - commonly known as MI6 - and UK intelligence agency GCHQ. Later, the Intelligence and Security Committee was set up in Parliament to have statutory oversight of UK intelligence.

Today, MI5 has its own Instagram account and its boss gives interviews to the media.

BBC 29 December 2023

https://www.bbc.com/news/uk-67835095

GCHQ, the United Kingdom's intelligence, cyber and security agency,

is based in Cheltenham, England.

CNN 14 December 2023

https://edition.cnn.com/2023/12/14/uk/gchq-spy-christmas-card-puzzles-2023-intl-scli-gbr/index.html

MI5 head warns of 'epic scale' of Chinese espionage

The heads of US, UK, Australian, Canadian and New Zealand security agencies come together

BBC 18 October 2023

https://www.bbc.co.uk/news/uk-67142161