Tonight Channel 4 broadcast an explosive documentary about Prince William and Prince Harry.

Typically for Channel 4 it covered a lot of “toff” activities, like hunting and polo in a deliberately disparaging way, and hyped up every glitch and problem that the Princes endured in their youth.

More interesting were journalist Richard Kay, who was close to their mother Diana, and James Whitaker, the Mirror photographer and lately pundit on all things Royal.

Richard Kay suggested that William is using Kate Middleton as a kind of decoy to cover his other activities. Both Princes, he said, are reluctant Royals who don’t want to do the job.

Whitaker also pursued this line, saying that their decisions to continue in the military “were extraordinary” and indicated they were turning their back on Royal duties and, by implication, marriage.

William does not come out of this very well. We hear that Diana referred to Harry as King Henry because she felt he would be more able to handle the role.

Chelsy Davy’s recent split from Harry was spliced onto the end of the tape, but carried the same message: the Princes are not interested in settling down, and both girls now seem to be aware of that.

Royal Anecdotes has known this for some time, as regulars will know, but the most astonishing assertion, made by Richard Kay, is that Kate is a decoy for William’s private activities.

No doubt a lot of flak will be generated by this documentary, and by the main interviews in particular, so we will await the outcome without commenting further for the time being.

(Overseas readers may be able to watch it on the Catchup service under the title “What happened next”.)

Once again we enter familiar territory: will they, won’t they?

I refer, of course, to that pair of star-tossed lovers, Prince William and Kate Middleton.

They have spent some time together up in arctic Birkhall on the Balmoral Estate in Scotland, causing the usual flurry of anticipation and speculation in the British press and more distant publications around the globe.

I have held off writing about this because I have been here before. Many times before. Too many times before to want to go through the rigmarole again.

However, since events are coming to a head on Friday — Kate’s 27th birthday — and next week, when William begins up to seven years’ service with the RAF, Royal Anecdotes has to say something about the situation.

Firstly, I suspect William joined Charles and Camilla up in Birkhall because of the Queen’s wish not to have the second-in-line to the Throne following the playboy circuit abroad at a time of grave economic stress for her subjects.

The apparent invitation to Kate’s parents, Carole and Michael, may have been out of simple politeness. After all, their daughter has been left dangling for seven years. A Royal expression of favour would make a lot of difference to an ordinary family in extraordinary circumstances.

At the very least Kate’s loyalty deserves a word or two about their future prospects, if only to discourage that dismissive nickname, Waity Katie.

Of course, the elaborate build-up now may be just be a nice way of acknowledging her steadfast friendship without damaging her reputation. As the years of service go by, William would then feel free to find someone else. Kate would more than likely do the same. This feels more like a fanfare and send-off for a Prince about to dedicate a fair portion of his life to dangerous public service.

We won’t know until William is safely tucked up in his new training school. If it hasn’t happened then, it probably never will.

I have to say, there’s very little obvious activity suggesting a Royal engagement right now. But a low-key announcement can’t be entirely ruled out.

I confess to a deep sense of foreboding as I write these words. For we are now being fed a picture of just how much the Monarchy will change under the reign of the present Prince of Wales.

Prince Charles holding a Kendo stick in Japan

Monarchies need to adapt and change, of course, and when a new personality ascends the throne it may be the ideal moment to introduce difficult and systemic changes into the old institution.

These innovations may come sooner than we think. There is a whisper going around that the Queen may pass the mantle of Monarchy to her son and heir when he is 65 — a mere five years from now. Last week we heard her refer to his future Kingship in public for the first time.

As if to drive the point home, a steady stream of leaks and suggestions is being released by credible media figures.

The country has been informed that Charles will keep his promise to drop the “Defender of the Faith” subtitle, for the looser, and therefore less-Christian, “Defender of Faith”. Any old faith will do, it seems, as long as you believe in something.

The former Archbishop of Canterbury, George Carey, spoke out recently against “destructive changes” being made to the old constitution, which has proved its worth over time. He clearly senses a disestablishment of the Church of England.

Last week, a close friend of the Prince, Jonathan Dimbleby, suggested that Charles could become an “active” King, speaking out on issues close to his heart, like climate change, education, architecture and conservation. The Irish and German Presidents were singled out as examples he may follow. Although they are neutral politically, they do get involved in day-to-day discussions on policy matters.

Prince Charles already boycotts Chinese leaders because of their treatment of Tibet. He once called them “appalling old waxworks”. Imagine the political fury if he refuses to attend a State banquet for the President of one of the world’s most powerful trading nations, as he has in the past?

The difference between the Queen and the Presidents of Ireland and Germany is that they are elected by a franchise of the whole population. They have legitimacy for activism — and therefore unpopularity — within their constitution.

British Constitutional Monarchs are expected to follow the convention that they can speak out in private at the weekly meeting with the Prime Minister and warn of future consequences. Other than that, the role is purely ceremonial, except as a last resort longstop against tyranny.

If a King Charles were to take on a Prime Minister directly, he would be swiftly marginalized by crafty and practised political infighters. He wouldn’t stand a chance. His humiliation would be complete, especially under a Labour government.

The Monarchy will not last long under those circumstances. Everything the present Queen has built up as the “unifier of the nation” would be lost. Politicians would begin by destroying what is left of our constitutional checks and balances — as Blair and Brown have gradually done for the past 10 years.

The package of measures Charles’s team of helpers are placing in the media, combined with the almost certain crowning of Camilla, could result in a serious dip in popularity for the Monarchy.

Other countries, over which the Queen now reigns, may decide to dump the Crown as well, leading to a crisis for the new King that could be impossible to contain.

His friend the 14th Dalai Lama was prophesied to be the last leader of Tibet. He is now an exile outside his country.

Will Prince Charles be the last Monarch of the United Kingdom, itself under threat from Scottish nationalism?

There are dangerous shoals ahead for the Prince. Shoring up what he has got may be a better path to Kingship than challenging the people’s representatives. In the end, influence is a more durable form of governance than power itself.

With the Prince of Wales’s 60th birthday looming tomorrow, Friday, celebrations got off to an exuberant start last night with an evening of comedy at the New Wimbledon Theatre, London.

John Cleese, of Monty Python fame was the master of ceremonies for the evening together with former Fawlty Towers co-star Andrew Sachs, Manuel to his fans. The idea was to give Prince Charles a very special occasion in the presence of a host of comic superstars.

Meanwhile, over at the BBC, an excellent documentary cum interview with the Prince was broadcast last night. It was conducted by Robert Hardman of the Daily Mail and examined every aspect of Charles’s life and charity work. The range of subjects over which Charles presides with great aplomb and expertise must be mind-blowing to anyone who doesn’t keep up.

Tonight, a dinner, with an orchestral performance, will be given by the Queen in honour of her son and heir. Yesterday, she was heard to praise his public-spirited work for charity and even referred glancingly to his future role as King, which is not something she normally mentions in public.

In these depressive times, you would expect the famously frugal Monarch to cut costs even at such a banquet. And indeed the wines selected by the Queen to enhance the Balmoral salmon and venison dishes, are notable but not lavish.

Puligny Montrachet Les Olivier Leflaive, 2006 at £40 ($60) a bottle, will refresh the palette without exciting aficionados of fine wine. The red, Chateau Leoville-Barton St Julien, 1988, around £100 ($150), will be excellent after a few glasses of the white.

The dessert wine is a nice 1996 Sauternes, and a suitably expansive note to end on.

The absence of conductor Riccardo Muti owing, apparently, to a disagreement over the length of his proposed programme and perhaps his fee, will not dampen spirits at what should be a glittering event.