Documents newly uncovered at Kelburn Castle offer a glimpse of the political machinations and jockeying for power which accompanied the descent into madness of King George III in the 18th century.

He was Britain’s longest serving monarch whose reign was overshadowed by mental illness and the enforced creation of a regency for his scheming son.

Letters discovered in the local castle archives show the extent to which paralysis gripped parliament and the exercise of power during the dying days of the King’s rule.

The present Lord Glasgow, Patrick Boyle, said the documents represented an important addition to the history of the period and he was fascinated by the insights the letters provided.

They came to light because the archive is being relocated to a dedicated room at Kelburn Castle, and, as part of that process, all of the documents are being reviewed and categorised.

It is believed the monarch, whose illness was dramatised by Nigel Hawthorne in the Oscar winning film, The Madness of King George, suffered from porphyria, an inherited group of metabolic disorders whose symptoms include paralysis, delirium, hypertension, and acute pain.

The first signs of the disease occurred in late 1788 when the King became confused, incoherent and agitated.

At the same time, the king and his Prime Minister, William Pitt the Younger, were involved in a political struggle with the Whig Opposition leader, the Duke of Portland and his twin acolytes, Lord North and Charles James Fox, hated by the King but supported by his son George, Prince of Wales, the Prince Regent.

In January 1789 the King’s condition began to improve and, he appeared to have made a full recovery by March.

A letter to David Boyle, grandson of the 2nd Earl of Glasgow and a future Lord Justice General, from his friend James Adamson, in February 1789, states: “If the king shall continue to mend at the rate which the newspapers now give out, all the expectations and manoeuvres of what is still named the Opposition will prove in vain and pointless, or at least will bear a short-lived fruit, at any rate the Regent’s wings are so clipped that he cannot overshadow many of his friends.” A Regency Bill, authorising the Prince of Wales to act as regent, was introduced and passed in the House of Commons, but before the Lords could pass the bill, George III recovered.

In the following years the Prince of Wales continued to seek to embarrass his father by encouraging the Opposition and pleading for a separate income.

In late 1810, at the height of his popularity, George III became dangerously ill and by May of the following year, he was pronounced insane.

A letter from David Boyle, then Solicitor-General of Scotland, to his brother, Colonel John Boyle of Shewalton, reveals how he hoped to be given a seat in the Lords to support the king, but that his elevation depended on the monarch’s state of mind.

The letter, dated December 10, 1810 states: “I shall be wanting, in regards to you and my mother, were I not to communicate to you, but in the strictest confidence for reasons which must be quite obvious to you, that the double gown has been distinctly offered to me in consequence of the Advocate’s declination and that, taking all things into consideration, particularly what I know of my family and the concurring voice of my friends, I have been led to express my acquiescence in the arrangements.” He added: “You will however, be quite aware that all this depends entirely on the health of the King’s mind being re-established, which though for several days there was the stronger possibility of which less has been rendered by his state on the 6th of June a little more problematic.

“If he had continued as well as he was for several preceding days, I have no doubt a commission would have been signed to prorogue Parliament after which appointments may have been proceeded.

"But, if His Majesty is not as well as to warrant this by the 13th, the two houses must move towards a regency in which event all plans such as I have established will be blown up.” A follow-up letter written by David, again to his brother, the following day adds: “I have this morning received from Mr Dundas [Henry Dundas, 1st Viscount Melville] a few pages covering a letter for Lord Glasgow and desiring me to peruse and forward it.

“In this letter he states that the flattering hopes entertained of the King’s health in that a regency may be avoided are, unfortunately, removed to a distance and that they conclude the business must commence in the two houses on Thursday.

“He then states the strong inducements for an attendance of the members of both houses who feel an interest in the questions affecting, not only the King personally, but the public welfare and presses Glasgow’s [the 4th Earl, David’s cousin] coming up as a doubt exists as to the use of proxies.

“From this untoward change, the King having been so well on Wednesday as to lead to the expectation of his seeing ministers in 48 hours, the less we therefore say on the subject the better and, except for speaking with the Advocate and Chief Baron as was necessary, I have mentioned it to nobody but my wife.” David Boyle was duly ennobled in 1811, appointed a Senator of the College of Justice, with the title Lord Boyle. He was Lord Justice Clerk from 1811 to 1841 and Lord Justice General from 1841 to 1852. He became a Privy Counsellor in 1820.

George III accepted the need for the Regency Act of 1811 and the Prince of Wales acted as Regent for the remainder of George III’s life. Despite signs of a recovery in May 1811, by the end of the year George had become permanently insane and lived in seclusion at Windsor Castle until his death.

In a letter from David to his brother John on July 16, 1811, he states: “I fear the King is now in a very doubtful state as to a resumption of power which, of course, will make ministers more cautious with the regent.” There are no plans for the letters to go on display at Kelburn Castle, principally because they are so fragile and valuable that there are concerns about them being damaged.