Realising that they were likely to be attacked, Charles’s men began strengthening the city’s defences. Earth was piled up against the medieval stone city walls to dampen the impact of cannon balls, and a large earth fort, dubbed Fort Royal, was thrown up outside the city’s Sidbury Gate to defend the eastern approach to Worcester. Much of this work was done by forced labourers from surrounding villages. Six months later, they would be set to work again, this time to demolish the defences they had been made to dig.

By now, Charles probably had about 12,000 men under his command in Worcester. About 10,000 were Scottish, the rest English. By 17th-century standards at least, this was a substantial force, but it was dwarfed by the massive army that the English parliament was preparing to deploy against it. Commanded by Cromwell, it was a mixture of regular troops and soldiers from various local militias and, at 28,000 strong, it was one of the largest armies ever to take the field in England.

Crushing defeat

On 2 September, Charles’s forces suffered a further blow to their morale when the Earl of Derby, the leader of the one English rebellion in support of the would-be monarch, turned up at Worcester with the news that his little army had been crushed at Wigan in Lancashire.

On the same day, in a bid to at least improve the clothing of his tattered army, Charles ordered £453 worth of cloth from a local draper. But there would be no time to make this into uniforms for, on 3 September, Cromwell’s mighty war machine rolled into action. The significance of the date wouldn’t have been lost on Cromwell’s men. It was the first anniversary of his great victory at Dunbar and, to underline the point, the English used the same rallying cry – ‘The Lord of Hosts’ – as they had at that battle. For anyone who knew their Bible (and many did), the message was clear. ‘The Lord of Hosts’ was taken from a rather ominous passage in the Book of Jeremiah which read, “This is the day of the Lord God of Hosts, a day of vengeance, his sword shall devour his enemies. It will be drenched with their blood.”

Seeking to make the most of his huge advantage in numbers, Cromwell planned to envelop Worcester from the south, east and west. The main drawback to this plan was a liquid one: running south to north past Worcester, the River Severn effectively cut his army in two, while troops advancing to the west faced an additional obstacle in the form of the River Teme, which joined the Severn just south of the city. But the English had found a solution to this problem in the form of a number of wooden boats, which they planned to lash together to form improvised pontoon bridges. While Cromwell remained with the bulk of his army on the eastern side of the Severn, his future son-in-law, Charles Fleetwood, led 12,000 red-coated soldiers in an attack in the west. The Scots fought hard, progress was slow and there was some bitter fighting in and around the village of Powick just south of the Teme. (Ironically, this was the site of one of the earliest actions of the Civil War in England, when Royalist cavalry routed their Roundhead counterparts in 1642).

A bridge too far

Seeing what was happening and anxious to maintain momentum, Cromwell personally led three brigades of his army across the first pontoon bridge, which had been built across the Severn. Faced with this threat to their flank, the Scots fell back across Powick Bridge and took up new defensive positions north of the Teme. Once again, Fleetwood’s troops were faced with stiff resistance, but the Scots simply didn’t have enough men to defend everywhere. A new pontoon bridge was set up across the Teme, and using this, the bridge at Powick and another crossing further west, the English eventually broke through. Initially, the Scots fell back in good order, but as more and more Parliamentarians arrived on the scene, the retreat turned into a rout and they rushed for the town bridge across the Severn and the apparent safety of the city itself.

Watching these events from the tower of Worcester Cathedral, Charles believed that he still had an outside chance of victory. He reasoned that, in crossing the Severn to help Fleetwood, Cromwell had seriously weakened his forces to the east. Rushing down the tower’s steep spiral staircase, he gathered together what forces he could and led them in a desperate sortie out of Worcester’s eastern Sidbury gate. Three hours’ desperate fighting ensued as the Scots initially drove the Parliamentarians back from their positions around Perry Wood and Red Hill and even captured two cannon. Sensing an opportunity, Charles called on David Leslie, who had assembled his cavalry outside the city, to come forward and support him. But with no confidence in his men, Leslie never moved.

All is lost

For Charles, the game was up. His outnumbered troops could advance no further, and by now, Cromwell was transferring troops back across the Severn to join the fray. The Scots battled on, using the butt-ends of their muskets when they ran out of ammunition, but eventually they were driven back into the city. Cromwell’s men stormed into Fort Royal and fired its cannon into the mob of retreating Scots who, according to one onlooker, were now so desperate to escape that they were “readier to cut each other’s throats than defend themselves against the enemy”. The Parliamentarians charged into Worcester, hot on the heels of the fleeing Scots, but royalist resistance lasted just long enough for Charles to escape out of St Martin’s gate. Tradition has it that he left by the back door of his New Street headquarters just as some Parliamentarian dragoons were coming in the front.

Around 2,000 of Charles’s men were killed in the battle, which Cromwell called “his Crowning Mercy”. Most of the rest were captured. The Parliamentarians lost 300 men. Although Charles eventually escaped, Worcester shattered the Stuart cause for a decade. It also confirmed the political dominance of England, and Westminster in particular, over the rest of Britain, the effects of which continue to resonate today.

What happened next?

Oliver Cromwell was now the most powerful man in the Republic, but Britain remained deeply divided and there was little agreement over how the country should be governed. In 1653, Cromwell became head of state as Lord Protector, but was never able to secure widespread support for his regime and, ultimately, his power rested on the fact that he had the army to back him. After Cromwell’s death in 1658, his son and successor, Richard, proved incapable of holding the country together and, in 1660, Charles II was invited to return as monarch.

• Read more about the Restoration

This article was first published in the April 2017 edition of BBC History Revealed