420 years ago, a deadly conspiracy to kill Britain’s king nearly succeeded. What if it had worked?

It's the evening of 4 November 1605, and a search party has descended into the cellars beneath the Palace of Westminster. Among the stacks of firewood, they find a man, calm and composed, guarding dozens of casks of gunpowder.

That man was Guy Fawkes, and within hours from him being found, he was due to light a fuse that would have upended English history.

The discovery of Fawkes foiled the conspiracy and exposed a broader network of Catholic conspirators whose aim was to blow up King James VI and I, along with his government, during the ceremonial opening of parliament. The Gunpowder Plot, as it came to be known, had failed.

But what if Fawkes had succeeded? As Professor John Cooper explains on the HistoryExtra podcast, the explosion would have changed the course of British history overnight.

The explosion that would have destroyed Westminster

Thirty-six barrels of gunpowder had been smuggled into the undercroft beneath the House of Lords; more than enough to obliterate the heart of English government.

“If it had all ignited,” explains Cooper, “it would have created an almighty explosion, certainly sufficient to destroy most of the Palace of Westminster.”

“The House of Lords would have been blown to pieces,” he continues. “The House of Commons across the courtyard would also have gone. Westminster Hall would also have been very badly damaged.”

Calculations suggest that the blast radius might have even reached parts of Westminster Abbey. “So we're talking about an almighty explosion,” Cooper notes.

A kingdom without a king

But it wasn’t just the buildings. It was the hundreds of prominent people inside who were the real target, including King James VI and I.

“It would have killed the people seated in the House of Lords: the peerage, the Privy Council, bishops and senior judges,” says Cooper. “It would have killed the king, and the heir, and the government, and all of the judges, as well as most of the nobility, most of the House of Commons, all in one go. It would have completely decapitated English society in one fell swoop.”

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The result would have been unprecedented chaos. The blast would also have filled the air with deadly gases, so even survivors of the initial explosion might have suffocated in the fumes that followed.

With the royal succession destroyed and the machinery of parliament obliterated, there would have been no clear centre of power left in England. So, what would have happened next?

How government might have collapsed

“It’s actually very difficult to imagine what would have happened if the Gunpowder Plot had succeeded,” Cooper says. “It could have gone one of two ways. The local systems of the shrievalty, the sheriffs, and the lord-lieutenancy were sufficiently robust that government would have continued at a county level until some sort of solution was found. That's one possibility.”

Those sheriffs and lord-lieutenants, appointed by the Crown, were responsible for enforcing justice, collecting taxes and raising local militia. While many would have been killed, those who escaped the blast might have tried to maintain order until a new monarch was named.

But as Cooper notes, there’s another possibility: “Or the whole system would have folded in on itself, and actually a lot of those sheriffs and lord-lieutenants would have been at Westminster for the opening of Parliament.” If they too perished, the country’s administrative network would have vanished.

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It was highly possible that England could have descended into panic and chaos, collapsing into crisis with no precedent since the Wars of the Roses.

And that wouldn’t have been the end of it.

Cooper says that religious violence almost certainly would have exploded throughout the country.

A spark for religious civil war

“I think there was a very strong chance that a religious civil war would have followed on from the Gunpowder Plot,” Cooper argues.
The Gunpowder Plot grew out of decades of religious tension. Since Henry VIII’s break from Rome in the 1530s, English Catholics had faced persecution and heavy fines for refusing to attend Protestant services. Under Elizabeth I, Catholic priests were executed as traitors. James VI and I initially adopted a softer stance but largely maintained continuity with the precedent set by his predecessor.

The conspirators, led by Robert Catesby and including Fawkes, believed that killing the king would open the way for a Catholic restoration. But by 1605, England had changed from its recent Catholic past.

“That long reign of Elizabeth had really changed the religious and social fabric of England,” Cooper explains. “Protestantism was deeply embedded in the English establishments – among parliamentarians, amongst lawyers and in the universities – but also among a lot of ordinary people. There was a lot of popular Protestantism that also at its edges connected with anti-Catholic sentiment.”

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Had the plot succeeded, Protestant England would have seen it as evidence of a Catholic conspiracy to destroy the nation. Retaliation would have been inevitable, with local uprisings, reprisals and massacres on both sides. England could have slipped into the kind of sectarian warfare that was already consuming parts of continental Europe during the Thirty Years’ War.

The puppet monarchy that never was

But what were the plotters themselves hoping for beyond wanton chaos? Despite their revolutionary and regicidal intentions, they certainly weren’t republicans.

“The principle of monarchy was very strong,” says Cooper. “The Catholic plotters were not trying to set up some kind of republic. Their thinking is entirely monarchical. They're trying to put in a substitute Catholic puppet monarchy, but it's still a monarchy.”

Their intention was to replace the Protestant dynasty, not abolish kingship itself. In the confusion after the explosion, they hoped to kidnap Princess Elizabeth, the king’s daughter, and crown her as a Catholic monarch under their control. Instead, the failure of the plot reinforced Protestant unity and the divine authority of the crown.

Looking back, Cooper calls the conspiracy “a fantastically audacious operation […] There’s something horribly spectacular about the level of vision, the level of hubris and the violence that the Gunpowder Plotters were prepared to consider.”

John Cooper was speaking to Danny Bird on the HistoryExtra podcast. Listen to the full conversation.