Ask most children in England what happens on the 5th November and they would tell you that it is Guy Fawkes night. It is a night we commemorate when in 1605 some Catholics in England expecting the new Stuart King – James to be more tolerant of them had decided to kill him. Their hopes were dashed when he had proved to be the opposite and had ordered all Catholic priests to leave England.

This so angered some Catholics that they decided to remove James and put his daughter Elizabeth on the throne ensuring that she was a Catholic.

This led to a plot to assassinate the king of England, but as we shall see it would devastate a sizeable area of Westminster and also kill everyone sitting in the Houses of Parliament at the same time as the James opened Parliament on 5th November 1605.

Guy Fawkes and his fellow conspirators had rented out a house next to the Houses of Parliament and managed to get 36 barrels of gunpowder into a cellar under the House of Lords.

For an unexplained reason, it was decided this year to search the cellars prior to the opening of Parliament and Guy Fawkes was caught red-handed.

In celebration of his survival, James ordered that the people of England should have a great bonfire on the night on 5th November. This fire was traditionally topped off with an effigy of the Pope rather than Guy Fawkes. His place at the top of the fire came in later as did fireworks. The East Sussex county town of Lewes still has the pope alongside Guy Fawkes when it comes to the effigies being burned.

Many conspiracy theories surround the 5th November plot but the use of gunpowder is an intriguing one.

The government had a monopoly on gunpowder in this country and it was stored in places like the Tower of London. How did the conspirators get hold of 36 barrels of gunpowder without drawing attention to themselves?

How was the gunpowder moved across London from the Tower of London to Westminster (at least two miles distant) without anyone seeing it? The River Thames would not have been used as it could have lead to the gunpowder becoming damp and useless. Thirty-six barrels would have been a sizeable quantity, estimated to be 2,500 kilograms, being moved without causing suspicion.

Experts from the Centre for Explosion Studies, at the University of Wales, Aberystwyth have estimated the Westminster Abbey would have been destroyed and the blast zone would have stretched as far as modern-day Downing Street.

They found that within a radius of about 40 metres, everything would have been razed to the ground. Within 110 metres, buildings would have been at least partially destroyed. And some windows would have been blown out even as far as 900 metres away.

In the 2005 ITV programme The Gunpowder Plot: Exploding The Legend, a full-size replica of the House of Lords was built and destroyed with barrels of gunpowder. The experiment demonstrated that the explosion if the gunpowder was in good order – and there is no reason to believe otherwise as Guy Fawkes was an explosives expert – would have killed all those in the building. The power of the explosion in the experiment was such that the 7-foot deep concrete walls (replicating how archives suggest the walls of the old House of Lords were constructed) were reduced to rubble. Measuring devices placed in the chamber to calculate the force of the blast were themselves destroyed by the explosion; the skull of the dummy representing King James, which had been placed on a throne inside the chamber surrounded by courtiers, peers and bishops, was found a considerable distance from the site. According to the findings of the programme, no one within 330 feet of the blast could have survived. The explosion would have been seen from miles away, and heard from further away still. Even if only half of the gunpowder had gone off, everyone in the House of Lords and its environs would have been killed instantly.

The programme also disproved claims that some deterioration in the quality of the gunpowder would have prevented the explosion. A portion of deliberately deteriorated gunpowder, of such low quality as to make it unusable in firearms, when placed in a heap and ignited, still managed to create a large explosion. The impact of even deteriorated gunpowder would have been magnified by its containment in wooden barrels, compensating for the quality of the contents. The compression would have created a cannon effect, with the powder first blowing up from the top of the barrel before, a millisecond later, blowing out. Calculations showed that Fawkes, who was skilled in the use of gunpowder, had deployed double the amount needed.

As a curious footnote, some of the gunpowder guarded by Fawkes may have survived until recently. In March 2002 workers cataloguing archives of diarist John Evelyn at the British Library found a box containing a number of gunpowder samples, including a compressed bar with a note in Evelyn’s handwriting stating that it had belonged to Guy Fawkes. A further note, written in the 19th century, confirmed this provenance, but in 1952 the document acquired a new comment: “but there was none left”.

A version of this post was published by CabbieBlog on 5th November 2012