Robert Armstrong, known as Lord Armstrong of Ilminster, has passed away at the age of 93. He was a remarkable figure in British politics and occupied some of the most influential roles in Whitehall, where he was known for his loyalty and discretion. He served as private secretary to Home Secretary Roy Jenkins in the Labour government and later worked under both Conservative Prime Minister Edward Heath and Labour Prime Minister Harold Wilson. Mr Armstrong became permanent secretary at the Home Office from 1977 to 1979 and eventually reached the top position in Whitehall as cabinet secretary from 1979 to 1987, serving most of Margaret Thatcher’s premiership.

One of the most notable moments of Mr Armstrong’s career came in 1986 when he appeared as a key witness in the Spycatcher trial. His testimony brought the phrase "economical with the truth" to international attention. It was during the trial that his approach to confidentiality was called into question, as he strongly believed that civil servants should remain silent even after their retirement. He argued that such confidentiality was even more important when dealing with members of the security and intelligence agencies.

Throughout his career, Robert Armstrong developed a strong personal relationship with Edward Heath. They shared a love of music and both were accomplished pianists. After Heath’s death in 2005, Mr Armstrong became the first chair of the Sir Edward Heath Charitable Foundation. He defended Heath against allegations of sexual abuse, stating that he had never heard anything to suggest such behaviour.

Mr Armstrong was born in Headington, Oxford, and had a privileged education at the Dragon School, Oxford, Eton, and Christ Church, Oxford, where he studied classics and philosophy. He leaves behind a legacy as one of the most dedicated and discreet civil servants in British history.

Armstrong will always be remembered as an influential figure during the Thatcher administration. He was content to remain in the background, providing advice to the prime minister on the importance of secrecy and encouraging fellow Whitehall officials to take a firm stance against leaks.

Despite his preference for staying behind the scenes, Armstrong was involved in a number of high-profile incidents that threw him into the public eye. He was tasked with investigating the Westland helicopter affair in 1986, determining that Leon Brittan, the Secretary of State for Trade and Industry, had leaked a letter that damaged Michael Heseltine, the Defense Secretary. However, he failed to disclose that Thatcher was aware of the situation.

During a hearing with the Commons defense committee, Armstrong was asked if Thatcher’s statement to members of parliament that she had allowed "accurate information to be made public" was at odds with the official narrative. Armstrong acknowledged that her statement was inconsistent with an earlier statement in which she claimed no information was sought or received. Armstrong explained away the discrepancy as a slip of the tongue.

Armstrong’s staunch defense of official secrecy led him to adopt an absolute constitutional doctrine that prevented government officials from whistleblowing or publicly criticizing government policies. In response to the Clive Ponting case, in which a man was accused of violating the Official Secrets Act by leaking information about the Belgrano’s movements during the Falklands war, Armstrong dismissed the notion that civil servants could appeal to the "public interest."

He produced new guidelines on the duties and obligations of government officials, arguing that civil servants were "servants of the Crown," but that the "government of the day" represented the crown for all practical purposes. Thus, civil servants had no constitutional ties to Parliament and could not appeal to a greater "public interest."

Thatcher sometimes ignored Armstrong’s advice, such as when he suggested that Jimmy Savile should not receive a knighthood. Armstrong felt that "things were not quite right," and noted that Savile had not denied the reports published in the press about his personal life. Armstrong’s instincts proved correct.

Armstrong appeared to be warmer and more sensitive than he allowed the public, or his colleagues, to see. He also had a dry sense of humor. One directive he wrote to senior Whitehall officials expressing frustration over leaks was itself leaked. Armstrong, when asked about it during an interview, replied with a wink, "I was disappointed it took six weeks to leak. I was hoping it would happen much sooner."

He was knighted in 1978 and made a life peer ten years later, serving as a crossbencher in the House of Lords. He was appointed chairman of the Victoria and Albert Museum trustees and a non-executive director of several companies, including BAT Industries, NM Rothschild and Sons, Rio Tinto, Shell, Lucas Industries, Carlton Television, and the Bank of Ireland.

Armstrong’s passion outside of Whitehall was music. He was a secretary and later a board member of the Royal Opera House from 1968 to 1993. He once said he tried to write his cabinet minutes in sonata form, with an exposition, development section, recapitulation, and coda. When appearing on BBC Radio 4’s Desert Island Discs, his luxury item was music manuscript paper, a pencil, and paper.

Armstrong married Patricia Carlow in 1985, and she survived him. Jane and Teresa, his two daughters from his first marriage, to Serena (neé Chance), also survive him, despite the couple’s divorce.