The Burrell media war has shown up the flaws of a hereditary head of state

It's been a bad week for the monarchy. In terms of their content, Paul Burrell's revelations in the Daily Mirror are remarkably restrained. He has revealed very few of the extraordinary secrets he must know. He is not responsible for the most sensational allegation to have surfaced this week: namely that St James's Palace covered up an alleged rape of a royal servant by an associate of Prince Charles and paid the victim to keep quiet. Nevertheless, the effect of the media war over his story has been deeply damaging to the institution Mr Burrell – and the papers – claim to support.

The tabloid frenzy has turned the monarchy not so much into a soap opera as another source of celebrity hysteria. Rival newspapers take opposite sides over famous people's private lives and remorselessly dissect them for the public's voyeuristic pleasure. Celebrities' popularity depends upon which paper the public reads, and how their stories are spun by rival publicists. All this may be an entertaining diversion when the subjects are chat show hosts. When it is the monarchy it brings the whole British constitution into question.

Looked at rationally, heredity is an absurd principle on which to base a head of state. It works only if the monarch and his or her household are seen to be entirely above the fray of media life – both political and personal. Once the sovereign's political views become known, or the Royal Family's private troubles become the currency of media rivalry – let alone when allegations of rape and cover-ups are made – the principle of a hereditary head of state starts to look extremely shaky.

Why? Because there is no escape route. Any of the damaging allegations and revelations of the last week could have happened to an elected head of state. But in those circumstances a constitutional president would almost certainly stand down. They would either come to the end of their elected term and then quietly leave office; or in extreme cases they could be forced to resign. But neither option is available to a hereditary monarch and Royal Family.

Over the past few years commentators have called for the monarchy to be "modernised". Many of these people championed Diana for starting this process. But the idea of the "people's princess" is a contradiction in terms. The principle of monarchy cannot be subject to the whims of celebrity. Celebrity is brittle: its power is entirely dependent on the fickle media and the public. Once the monarchy becomes dependent on public opinion – but without the escape mechanism of replacement – its constitutional foundations are eaten away. For whereas under a president (as we saw with Clinton) the individual's reputation may be tarnished but the institution survives intact, under the hereditary principle the two are inextricably intertwined.

The Queen realised this long ago, of course, which was why she was so disturbed by the Diana effect. But it has now inexorably dragged her down too.

And so the triumphalism of the royalists' camp after the Queen Mother's funeral and the Golden Jubilee is seen to be misplaced. As the wisest of them knew, public opinion is not the court in which monarchy should be judged.

As yet we have had no polling evidence on the effect of this week's events on public support for the monarchy. But it is hard to think that it could have been anything but disastrous.

The monarchy will survive, of course, because very few people have the appetite for the huge historical rupture that would be its abolition. But the events of the past week have surely made some kind of "cleansing" reform process more likely. This will not be easy. For example, calls this week for the law to have "The People" bringing cases to court rather than "Regina" will founder on the basic problem that "The People" don't exist in our constitution, which sees us as subjects of the Crown, not citizens. But if at least a debate about constitutional reform gets kick-started, then some good will have come out of this unholy mess.

Michael Jacobs is general secretary of the Fabian Society, whose Commission on the Future of the Monarchy reports next spring