Tensions in central London are high. Blundering its way through the streets, seemingly oblivious to the demonstrations, the royal vehicle is soon surrounded. It struggles to push its way through the wall of angry protesters. There is a great deal of shouting. Republican sentiments are expressed. Objects are hurled and one of the vehicle's windows is shattered.

The scene I am describing may sound familiar but it is yesteryear's news rather than yesterday's. In fact, it was 215 years ago. The vehicle was not a Rolls-Royce but a horse-drawn carriage and it was carrying not Prince Charles but King George III.

In October 1795 the king's coach was mobbed as it made its way to the state opening of parliament. Britain had been at war with revolutionary France since 1793 and the conflict's unpopularity grew as it placed the nation under increasing economic strain. The summer had witnessed food shortages in many parts of the country. The protesters called for "peace" and for "bread". Some went further; their cry was "Down with George! No King!" Stones were thrown at the carriage. One of them shattered a window near where the king was seated.

The protesters viewed the king's body as a symbol of the state with which they were deeply disenchanted. They viewed the gilt carriage that sheltered that body from the grim realities of the city streets as the sign of a government that was deaf to the people's suffering. As the scenes of Thursday last week vividly demonstrated, two centuries of politics, of the rise of liberal democracy and the decline of monarchical power, have done little to alter the power of this symbolism.

There is, of course, no photographic record of the attack on the royal carriage. But the great satirical cartoonist James Gillray does provide us with an enduring image of the event. The Republican Attack shows the vehicle besieged and damaged, the faces of two of its passengers (though not of the king himself, who seems absurdly impassive) etched with fear – details that are remarkably redolent of the pictures of the shocked Charles and Camilla, and of their paint-spattered Rolls-Royce, that have assumed such symbolic value over the past few days.

In 1795, as in 2010, a broken window was the worst of the violence. The king reached his destination unharmed. But the Tory government's response to the attack on the royal coach was long-lasting. William Pitt the Younger's administration was especially concerned with the swelling number of radical activists in London in the wake of the French Revolution of 1789, but its efforts to curb the spread of revolutionary politics had largely been frustrated. A year earlier, in November 1794, the government had put three radical leaders on trial for treason. All were acquitted.

The attack on George III's carriage was the just pretext Pitt needed to introduce legislation that would finally cripple the radical movement. He also read the king's body as a symbol: not of an unjust state but of a dangerously imperilled one. Claiming that the carriage's window was shattered by a bullet rather than a stone, the Tory administration rushed two new bills through parliament in under two months. The first, the Treason Act, clarified the legal definition of high treason (with which the government's case had come unstuck in the 1794 trials); the second, the Seditious Meetings Act, prohibited public gatherings of more than 50 people without a magistrate's licence. They were dubbed the "Gagging Acts".

At a glance, Gillray's cartoon appears to side with the government's version of events. But look again. In the bottom right, the figure of Britannia has been trampled under the horses' hooves. This is a hit and run, and at the reins of the carriage is none other than William Pitt who drives his administration on blindly and ruthlessly, insensible to the irreparable damage he is inflicting. The nation is the casualty here, not the royal passenger. The government, not the protesters, are the real hooligans. I wonder what Gillray would have made of last week's events?