THE British Constitution was once the envy of the world. Well into the middle decades of the 20th century its canonical texts – from Magna Carta and the Habeas Corpus Act to Dicey and Bagehot – were studied, admired and emulated wherever the British flag flew over a dominion, colony, coaling station, trade post or remote island mission.

Whatever the British Constitution once was, it is no more. Like the Empire that nourished it, the great house has fallen. The grandeur of its 18th century columns, the sublime intricacies of its gothic Victorian follies, its ambitious 20th century modernist extensions – all these have crumbled through neglect, until only the rubble remains.

What worm-eaten rubble it is: grubby sleaze, putrid corruption, brazen lies, grotesque incompetence and shameless irresponsibility.

Lack of proper maintenance is partly to blame. It is the duty of every generation to care for that which has been entrusted to them, to preserve their heritage, to renovate and repair before it is too late. This was not done.

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In 1911, when the Parliament Act was passed, it referred to an intention to replace the House of Lords with a chamber “constituted on a popular instead of hereditary basis”. In 1917, a Speaker’s Conference recommended a system of proportional representation, but the Government refused to back the reform and it was killed off in the Lords. Real home rule of Scotland was twice proposed in the 1920s, but nothing happened.

By the late 1960s Quintin Hogg, then the Conservative Shadow Home Secretary, had proposed a judicially enforced Bill of Rights. Charter 88 – a balanced, sensible programme for essential, overdue constitutional upkeep – was signed nearly 35 years ago but left to languish. In 1991 the Institute for Public Policy Research published a draft constitution which, if not excellent, was at least very good – but nothing came of it.

Time and time again, the opportunities to fix the roof while the sun shone were squandered. Finally, when it became clear that there was no alternative but to do something, we hired the cheapest, least qualified odd-job man possible. To put it in terms Fawlty Towers fans will appreciate, Tony Blair did the constitutional equivalent of using a wooden lintel in a supporting wall. All his reforms were shoddy half-jobs, which tore down the old without properly constructing the new. Since then, we have been looking for “a screw jack to prop it up before the whole bloody lot comes down”.

The National: Former prime minister Tony Blair

The mortar that held up this venerable pile of traditions, charters, statutes, precedents and conventions was the “good chaps” theory – the idea that everyone could be trusted to do the right thing, to act with self-restraint, to respect the principles of justice and fair-play, to do what is “done” and not do what is “not done”.

The maintenance necessary was as much moral as institutional. This was recognised by the Victorian jurist Sir James Fitzjames Stephen. Writing in 1873, he argued that the defects of the British system could be borne with. “So long as political life is the chosen occupation of wise and honourable men”. If “the personal character of politicians should ever be seriously lowered”, Britain’s lack of a written constitution “would give bad and unscrupulous men a power for evil hardly equalled in any other part of the world”.

This moral aspect too has been neglected. We have always been governed by Etonians. Some say we have never been governed by an Etonian as morally reprehensible as this one. It is as if the opening passages of Book 1 of Cicero’s De Republica have not been properly hammered into him.

One remaining moral prop is the Queen – who is widely believed to set a good example of selfless dedication and public service, and to provide frank, informal but occasionally chiding counsel to her Prime Ministers.

For some, the Queen serves as a “substitute constitution” – source of legitimacy and identity. The Queen is the last link to what Britain once was, the last living remnant of Empire, the last relic of a past where public life could be morally regulated by the silent tut and the almost imperceptibly raised eyebrow. Queens, however, do not live forever. What happens when she dies?

No one knows what the current British state is, or how it works, under anyone else but her. Her successor is a divisive figure. He has also been chomping at the bit to exercise power for decades. How will our hollowed-out institutions adapt to this new situation?

The moral and constitutional order which the Queen embodied has been hanging on by a thread for some time. The Queen’s death may be the final KerPlunk stick that makes all the marbles tumble. Once she is gone, all the constitutional questions that have been papered over, delayed and bodged for that last century will be laid dangerously bare.

Professor Donald Christie is next week’s guest on the TNT show. Join us at 7pm on Wednesday. The TNT show is live and it’s free. So, no licence, no problem