Pageantry, pomp and two institutions dressed up to the nines but some way past their best

The state opening of Parliament is more than just a treat for tourists and David Dimbleby. Its pageantry and tradition, its absurd rituals and archaic office-holders, its antiquated costumes and, above all, the central role of the monarch herself are a reminder of a time when the crown, in the words of the great constitutionalist Walter Bagehot, gave "a vast strength to the entire constitution, by enlisting on its behalf the credulous obedience of enormous masses".

Such ancient habits died hard. As late as the 1950s, many people believed that the Queen and her family had been placed on earth through some form of divine intervention. We have long since seen the end of credulous obedience and total deference. Public enthusiasm for the monarchy has declined to such an extent that large numbers of people are not just sceptical about the institution, but embarrassed by it. No longer can it be bragged that our monarchy is the "envy of the world". The rise in popularity of the monarchy after the death of the Queen Mother and the Golden Jubilee appears a blip on a trend of inexorable decline.

Much of this is the fault of "the Firm" itself. Which of its directors – the Queen, Prince Phillip, the Prince of Wales – carries the greater share of responsibility for its strategic errors makes for entertaining speculation. But the errors were largely unforced, and their remedies implemented only in the face of public pressure. Hence the decision to pay income tax, so tardily arrived at in 1993; hence the failure to show more sensitivity after the death of Diana, in 1997, corrected only after the intervention of Downing Street. The late Princess continues to haunt the Windsors. Thanks to the catastrophic mishandling of the trial of her former butler, Paul Burrell, we have yet more deeply damaging insights into the royal household.

Among the more dispiriting aspects of the revelations was the picture that has emerged of Prince Charles; he seems a spoiled and stubborn character, and there must now be grave doubts over his suitability to succeed to the throne. For five years he and his aides have conducted a tireless campaign to rehabilitate him and nudge the public towards acceptance of his mistress, Camilla Parker Bowles. At the very least, this stands in ruins.

Over the years, the House of Windsor has proved inept at defending itself. This is unsurprising, when one catches a glimpse into its self-created cocoon of toadying and deference; it is out of touch with the modern world. And in this age of celebrity, its squirming manoeuvrings when caught in the public eye are painful to observe.

The Prince of Wales's appointment of his own private secretary to head an inquiry into allegations of misconduct and criminal behaviour at St James's Palace is risible. Sir Michael Peat is an honourable man; but he cannot convince a sceptical public that he is truly independent. The expectation is that Sir Michael's efforts will be a cover-up that rubbishes the previous inquiry. We know that because he has virtually said as much. A scapegoat will be found, possibly the Prince's solicitor, Fiona Shackleton. That will not be good enough; sooner or later, proper independent inquiries will have to be conducted into the Burrell prosecution and the Prince's court. True to form, however, the Windsors find it difficult to bow to the inevitable.

Viewed in a historical perspective, the travails of royalty are nothing new. British republicanism reached its peak in the 1870s, after Queen Victoria withdrew from public life following the death of Prince Albert; she rarely attended the State Opening of Parliament. Think of Charles II's 14 illegitimate children or Edward VII's prodigious gambling debts. Misbehaviour, in other words, has been the norm. With the exceptions of Charles I, James II and Edward VIII, monarchs have survived unscathed.

Whether we ever see Charles III or William V depends on a recognition, as the Queen remarked in her "annus horribilis" speech 10 years ago, that "no institution should expect to be free from the scrutiny of those who give it their loyalty and support, not to mention those who don't". At the very least, the events of the past fortnight have made that sizeable section of opinion, including this newspaper, that has hitherto viewed the monarchy with indifference think afresh about the merits of a republic.

Whatever the fate of Windsors, yesterday's Ruritanian activities also highlighted the weakness of one other venerable but more precious piece of constitutional machinery: Parliament. A presidential prime minister runs an all-powerful government that has no effective opposition and seems to have contempt for Parliament. Incredibly, Tony Blair published the contents of yesterday's speech in a Sunday paper. The debate in the Commons on the "loyal address" with its knockabout and old-fashioned language was a depressing irrelevance. What we saw yesterday were two institutions dressed up to the nines, but some way past their best. No wonder we're disenchanted.