One of the most turbulent and bloody periods in English history ended with the previously unimaginable spectacle of King Charles I’s public beheading. Our civil war and transition from Monarchy to a Commonwealth was effectively a military-backed regime change.

But just a decade later, the dead king’s son was restored to the throne and set about seeking institutionalised vengeance upon the judges, lawyers, gaolers and executioners who had dared to kill his father.

In his latest book Killers Of The King, historian Charles Spencer mines this dramatically fertile period of upheaval, focusing on the vilified ‘regicides’ who signed Charles’ death warrant.

Some fled into exile, others were incarcerated for life in grim prisons, while the unluckiest endured the grisliest of public deaths – hung, drawn and quartered – their privates hacked off and innards burned before their eyes while still alive.

Even Oliver Cromwell and chief judge John Bradshaw who had the temerity to die before the Restoration, were disinterred, beheaded and stuck on a pike outside Westminster Hall where Charles had been tried.

“I started the book with a view that I would end up being hugely sympathetic to Charles I as a victim of a kangaroo court, but, as I researched the extraordinary drama of the civil war it had thrown up, these intriguing, individuals whose stories were so fascinating and diverse. Getting to know some of the key regicides in greater depth meant I sympathised with them much more,” says Spencer, who despite being an Earl, would have sided with Parliament had he been alive at the time.

“I do believe the king had to die for England to have a hope of peace. He was impossible to trust and the one thing you had to be as a ruler was decisive otherwise you were too weak to survive. The whole of society was changing in a fundamental way and something drastic has to happen. Sadly for Charles it was being decapitated. But despite my feelings against him as a king, I have huge personal regard for him as a man, he was a gentle, church loving, chess playing figure. I feel very sorry for him, but I also think those who put him to death were very brave men.”

Spencer relates in pacy detail how officers of Cromwell’s elite New Model Army muscled aside dissenting MPs to create a scaled-down ‘rump’ parliament to try the king.

“The court was flawed in legal terms but these were extraordinary times.

“Charles was tried in the main by military officers and their cronies who decided they had to act quickly against the king, partly out of self-interest because a lot of senior officers died in the second civil war and if the war flared up again they would be fighting it, and partly because if they allowed the king to reach an alliance in the commons they might sacrifice the military leaders as scapegoats.”

Patriotic duty

Researching letters and diaries from the period, Spencer discovered few of the regicides felt personal animosity against Charles, but acted out of religious and patriotic duty.

“They were very devout men who believed it was their God-given patriotic duty to stop this blood-letting in what remains the most bloody conflict this country has ever been involved in.

“They pushed the execution through quickly and no-one believed it would actually happen until it did. When the king’s head was cut off there was a gasp of amazement from the crowd.”

A decade on, the ruthless hunting down of the regicides drew fire from the fact that half the population had supported the Parliamentarians.

“Someone had to pay for what had happened but you couldn’t punish everyone who stood against the king so they focused on those involved in the most heinous act of his judgement and execution.

“It drew a line under a traumatic period and helped everyone to breathe again.”

Centuries on, this turbulent period might also explain why we’ve contentedly settled for the compromise of a constitutional monarchy.

“I think it suits the temperament of the British people very well to have a not very powerful constitutional monarch who is easily identifiable, solid, dependable and non-threatening,” says Spencer, who via his sister Princess Diana, will one day will be uncle to our king.

“I also think what happened in the 17th century took the pressure off the whole idea of the monarchy as something absolute and stopped something more traumatic happening 100 years later as it did in France.”

Spencer, who studied English at Oxford, will be interviewed at the lit fest by Lady Antonia Fraser, whose bestselling book on Mary, Queen of Scots (Charles I’s grandmother) helped fire his passion for the subject.

“There was a book I read at prep school when I was eight (Rosemary Sutcliff’s) The Eagle of The Ninth, set in Roman England.

“That was the first moment I realised I liked history but I haven’t got an ear for creating dialogue so I couldn’t write historical fiction.

“Antonia’s book on Mary, Queen of Scots was the first proper history book I read and it fired my enthusiasm. She has led the way in writing the kind of book that I really want to read – and to write – not someone spewing dry dates and preaching but the kind of really good read that is very much character-based, where you can see the enormous amount of research but it’s not boring.”

Balanced

His own books, which include a personal history of the Spencer family and the award-nominated Blenheim: Battle for Europe, he hopes are similarly gripping – but also balanced.

“I like to find really interesting letters, diaries and court records and pick the best dialogue from them. I like knowing that I have absolutely covered every aspect of the research, then I like writing at great pace that really keeps the narrative going. I think my role as a historian and a storyteller is to tell the tale even-handedly.

“It’s very important that you keep your personal views out of it as much as possible and don’t twist the history to suit those views, that’s unfair on the reader and all those involved.”

Charles Spencer talks to Antonia Fraser on September 16 at 8.30pm.