The Prime Minister's appearance at the Leveson inquiry was enlivened by news that he had received a lunchtime phone call from his wife Samantha to fill in the details he simply couldn't remember about how often he had been hobnobbing with Rebekah Brooks, lately chief executive of News International, during weekends in Oxfordshire. "Mrs Cameron", as the PM referred to his spouse, "keeps perhaps a better weekend diary record than I do". "That's the great value of wives," Mr Justice Leveson remarked. "Indeed," replied Mr Cameron.

Eleven years ago, almost to the day, another court heard from a wife about a diary, obviously in very different circumstances. This was Jeffrey Archer's perjury trial at the Old Bailey when Mary Archer came to her husband's rescue by recalling that there was more than one diary in his office. In the event, Jeffrey Archer was jailed for perjury.

Before sentence, Jeffrey's barrister had pleaded: "He has not, in the conduct of his case, compounded any untruth ... by any evidence which he has given" – only to be interrupted bythe judge, Mr Justice Potts, referring to her last-minute testimony, asked: "What about the evidence from Lady Archer?"

Despite his four-year prison sentence, Jeffrey still retains the title of Baron Archer of Weston-super-Mare, is allowed to remain in the Lords, which is a law-making body, and is entitled to claim public money for his attendance.

Being Lady Archer can only have helped Mary's subsequent career, but the title was purely because she was married to a peer. Now she has been made a dame and has a title in her own right.

Suddenly, the woman who has spent much of her adult life defending and excusing a perjurer – she even launched a campaign to clear his name after his jailing (10 out of 10 for loyalty, nought for judgement) – is being celebrated as "a champion of patient care and safety" and dubbed "a Cambridge dignitary". Last week, she was chosen to have lunch with the Queen at a Diamond Jubilee celebration.

So, how did this transformation from loyal wife to near-saint come about?

We must give Dame Mary credit for 19 years as director of the Cambridge University Hospitals NHS Trust, 10 as its chairwoman, a demanding role for which she is eminently suited, being a scientist, fundraiser, and publicist. She owes her life to the skills of the NHS, after an operation recently for bladder cancer.

Though often in Jeffrey's shadow, she has always been an impressive person herself. Among her achievements are: being one of the youngest dons in England; a pioneer in renewable energy; president of the Guild of Church Musicians; and the first elected woman on the Lloyd's Council. Her life has not been entirely about sitting on boards and contributing to chemistry journals. She has a penchant for show business, and once sang "Who Wants To Be A Millionaire" at a Council of Lloyd's dinner. Now she can add "There is nothin' like a Dame" to her repertoire.

It was Mary's "fragrant" appearance during the 1987 court case that helped Jeffrey win libel damages of £500,000; and it was during her directorship at Anglia that she brushed off Jeffrey's share-dealing in the company as a "needless embarrassment", though it became a subject of a Department of Trade and Industry investigation.

As a dame, she intends to continue spending time chairing meetings of one sort or another. It would be churlish not to admire her head-girl diligence and public-spiritedness. But ... an honour?

Margaret Crick is the author of Mary Archer, For Richer, For Poorer (Simon & Schuster)