Monarchy gives a human face to government. A Royal Family, far more than a republic, embodies all the rituals of life with which we are most familiar — birth, marriage, death and other anniversaries and milestones. The familial makes familiar and trusted.

Our remarkable Queen has now set yet another record. She has overtaken Queen Victoria to become the oldest monarch in British history, at 81 years and 244 days. Achieving ever-greater age is not something that everyone enjoys, let alone boasts about: and this Queen boasts about almost nothing. If anything, she will think any recognition of this new milestone rather over the top. She considers it all in the line of duty — and duty, deeply unfashionable in today's Britain, is always her lodestar.

Robert Hardman, the author of an excellent new book, Monarchy, is stunned by the workload of the monarch. In an average year the Royal Family perform some 4,000 engagements, each of which involves at least 100 people. Hardman thus reckons that about half a million have some sort of royal encounter every year.

To a far greater extent than anyone realises, the Queen is integrated into the life of the country. She is an essential part of the warp and woof of society. That society has changed almost beyond recognition since she came to the throne and she has changed with it — perhaps hesitantly at first and with growing confidence in the past ten years. She understands better than anyone that for monarchy to survive it has to retain consent; and to do that it has constantly to evolve. Hardman quotes a senior palace official quoting Lampedusa's The Leopard: “If we want things to stay the same, things will have to change.”

Hardman describes the way she has quietly enabled the institution to change during her 55-year reign. In a recent visit to Brighton the Queen did not meet the sort of dignitaries that she would have honoured just a few years back: instead it was the Gay Elderly Men's Society, a swimming club and a crèche.

The one thing that remains unchanged is the sense of service. People recognise that in her. After the turmoil at the death of Princess Diana, and the abusive criticism of her in some tabloids, the Queen received thousands of letters thanking her for her constancy. Even republicans now know that her behaviour is above criticism. Roger Scruton, the philosopher, described her role well as “the light above politics which shines down on the human bustle from a calmer and more exalted sphere”.

The Queen's late, great private secretary Martin Charteris used to say: “May the Queen live for ever.” She may not do that but, she is doing the next best thing.

William Shawcross is writing the official biography of Queen Elizabeth, the Queen Mother.

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