The Queen at 90: behind the scenes our monarch is preparing for change

For Her Majesty, prior knowledge of possible dangers is something she not only prefers but also expects.

While our monarch’s great age is now the cause of celebration not only in this country but around the Commonwealth and wider world — with thousands of street parties planned and documentaries aired on television — courtiers have been doing their pragmatic sovereign’s bidding for some time.

Make no mistake, this is a monarchy in transition; a monarchy poised and ready for a change in management at the blink of an eye.

This was evidenced two years ago when Her Majesty’s most senior aide, her private secretary Sir Christopher Geidt, was awarded his second knighthood in the New Year’s Honours List. The citation read that it was for “a new approach to constitutional matters... [and] the preparation for the transition to a change of reign”.

It was a remarkable public admission and the clearest official sign yet that Her Majesty was getting ready to pass the mantle on to her son and heir, the Prince of Wales, currently 67.

I agree with constitutional commentators who say the Queen has no intention of abdicating. She saw the deep pain that abdication caused her beloved father, and the instability that threatened the country, when his brother Edward VIII gave up the crown in 1936 and became Duke of Windsor.

Then there is that famous broadcast on her 21st birthday in 1947 when she said: “I declare before you all that my whole life, whether it be long or short, shall be devoted to your service and the service of our great imperial family, to which we all belong.”

However, at this moment in time she is the not only the longest serving monarch but also the oldest, and we are undoubtedly in uncharted territory. Her consort is 95 in June too.

The Duke of Edinburgh said when he turned 90 that he was “winding down” and reducing his workload as a senior member of the royal family (although he still undertook more royal engagements in the last year than Prince William, the Duchess of Cambridge and Prince Harry combined).

In the same interview with the BBC, the Queen’s husband said: “I reckon I’ve done my bit,” adding significantly: “It’s better to get out before you reach the sell-by date.”

There is no suggestion the Queen feels the same way, but senior royal household sources both past and present have told me nothing has been ruled out.

Going forward, allowances will be made for Her Majesty’s age. The Prince of Wales and other members of the family will be expected to step up and represent her at public events more and more. That, after all, is the nature of monarchy.

But could she ever be persuaded to accept Prince Charles as a regent?

A senior figure who worked closely with the Queen for many years said: “That would really be a matter for the Queen, the Prince of Wales and Prime Minister. But I assure you if the Queen was so advised and felt she could not continue in her role in the way she wanted to, her sense of duty would kick in. She would only want what was is good for the country and the institution of which she is custodian.”

Abdication, according to those I have spoken too, would be a step too far. But a regency — where a prince rules in the absence or incapacity of a sovereign, as experienced under George III when he was too ill to reign — has to be a possibility at least.

After all, in a decade’s time, if the Queen were to live that long, could we really imagine a centenarian holding weekly audiences with her prime minister and working on her red boxes every day?

According to law, a regent can only be appointed if the sovereign is considered unfit to rule, by the written testimony of three or more of the following: their spouse, the Lord Chancellor, the Speaker of the House of Commons, the Lord Chief Justice of England and the Master of the Rolls.

These can also declare “that they are satisfied by evidence that the sovereign is for some definite cause not available for the performance of those functions”. That offers more than enough wriggle room for the constitutional lawyers, if needed.

Until 1937 our constitutional law had no permanent provision for a regent to cover the situation of a monarch being incapable of performing his or her duties.

It was the debilitating illness of the Queen’s grandfather George V, who suffered chronic bronchitis from 1935 until his death the following year, which led to the updated Regency Act. Since then no statutory regency has been created.

A regent could be appointed if the person inheriting the throne is under 18 or if the monarch is “by reason of infirmity of mind or body” incapable of performing the royal functions.

An intriguing addition is that phrase within section 2 of the Act which says a regency arises if “the sovereign is for some definite cause not available for the performance of those functions”. It is not clear what situations this covers.

European kings and queens abdicate routinely, slipping happily into the background and a quiet retirement. In 2013 even a pope, Benedict XVI, caused a storm when it was announced he would step down. It led to a familiar chorus: “It will never happen here.”

Only time will tell.