HENRY Neville, an English republican political theorist, described constitutional decay as being like “the French disease”.

In his 1681 tract, Plato Redivivus, he noted that it was easily cured, when hard to detect; but hard to cure, and possibly fatal, by the time it is obvious.

The distemper of the British state was ­evident, to the keenest observers, in the 1970s. Against the backdrop of falling economic ­performance and the collapse of the post-war ­social-democratic consensus, some ­identified the unbalanced, untamed and worn-out ­constitutional structure of the British state as being to blame.

This was the time when Lord Hailsham – the best and most perceptive constitutional ­thinker the Conservative Party has ever ­produced – ­criticised British institutions as being an ­elective dictatorship, and proposed a series of remedies including regional devolution, a reformed upper house and a proper bill of rights.

The National: Embargoed to 1700 Thursday March 05

File photo dated 6/5/2016 of a Conservative Party rosette. The UK's human rights watchdog is under increasing pressure to investigate Islamophobia in the Conservative Party after being handed a fresh dossier

Other good doctors to the body-politic also identified the disease and prescribed wholesome cures. The package of constitutional ­reforms laid out in the SDP-Liberal Alliance manifesto of 1983, Charter 88, and the Institute for ­Public Policy Research’s 1991 draft ­written ­constitution for the UK were all effective ­remedies, which if administered on time would have saved the life of the patient.

However, the symptoms were not yet ­obvious. Sure, the disease was evident enough if one examined the withered limbs of Glasgow ­shipyards or the sores of Fife mining towns, but those were easily concealed and did not bother middle-class people living within a hundred miles of London. So most ignored the signs, or hoped they would just go away.

It is not the well who need a doctor, but the sick. A patient who believes they are well can never be persuaded to take their medicine.

So it was after 1997, when unskilled ­physicians, realising that they could not administer a ­curing dose of reform, offered instead only ­homeopathic remedies: a Human Rights Act that was merely legislative and could not ­prevent the enactment of other laws contrary to the human rights it sought to protect; a Supreme Court that was not really supreme; a system of devolution in which the Scottish Parliament was likened, in constitutional terms, to “an English parish council”.

Now the illness is quite advanced. We see signs of it everywhere – in once healthy towns that are now pustulating with urban blight, in a state gangrenous with corruption at the ­highest levels, in a fever of distress that has spread throughout the economy. It is now too obvious to ignore.

Yet still there are quacks who deny that this has anything to do with the state’s poorly ­constitution. They blame Evil Wicked Tories, or austerity, or Brexit. Or perhaps, if they are on the other side of politics, they blame “wokery” or immigration. Some blame the breakdown of values like trust, decency and neighbourliness that once made life bearable.

Yet all these things are but the symptoms of a constitutional disease that has now ravaged the whole state. Irrational behaviour such as austerity and Brexit, the mouth-foaming British nationalism, the wild vomiting-up of authoritarian bile, are all just signs of the disease’s effects on the nerves, brain and organs. The delirious insanity in which we now live is but the final stage before death.

Sometimes I have to explain to people that I am “not that kind of doctor”, but when it comes to diseases of the constitutional system, I am qualified both to diagnose and to prescribe.

It is my duty to bring the patient bad news: there can be no cure without major surgery. It is too late for the pill of minor reform, of the sort outlined by Gordon Brown’s recent policy paper. Even the moderate remedies once ­prescribed, like a justiciable bill of rights, ­proportional ­representation, are no longer enough.

Any effective treatment now requires a full constitutional transplant; the removal of rotten, reeking constitutional tissue and its ­replacement by healthy organs.

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It is not as if there is any shortage of donors. There are examples of compatible constitutional bodies from many Commonwealth countries, which could be ingrafted with assurance that they would not be rejected.

What is not so certain is whether the ­British body-politic can stand such constitutional ­surgery without losing the Union. An amputation, like the separation of conjoined twins, might be necessary to save the life of both.

In other words, the prognosis for the ­United Kingdom is not good. Without major ­constitutional surgery, it is terminal. Yet that surgery is likely to be fatal to the Union.

For England, Scotland, Wales and Northern Ireland, the odds might be better – if serious steps are taken soon.

Whether we will have the courage to undergo such surgery, or whether we will keep ignoring it and die, remains to be seen. In 2014, 55% of people were more afraid of the operation than of the disease. Perhaps next time that will be different.