The news that his security experts are conducting an urgent review of the King’s safety during his expected traditional Christmas Day walkabout near his Norfolk home, Sandringham – where he will be accompanied by his wife – is sad but scarcely surprising.

Already in his short reign there have been two disturbing incidents: eggs were thrown at Charles during royal visits to York and Lincoln. Fortunately, the perpetrators missed both times. But, given the tendency for copycat behaviour among the more moronic of the monarch’s subjects, the danger that an egg thrower may score a hit next time is obviously high.

Compared to their European cousins and counterparts, and considering how frequent are their encounters with crowds, violence directed at Britain’s royal family has been mercifully rare. In 1981, during the Trooping the Colour ceremony, a teenage boy named Marcus Sarjeant fired blank shots at the late Queen Elizabeth from a starting pistol. He was grabbed by members of the public and later jailed for five years for treason.

King Charles will not want to withdraw behind high walls and heavy security screens

Earlier, in March 1974, a gunman named Ian Ball tried to abduct Princess Anne after stopping her car in the Mall as she drove to Buckingham Palace. Ball shot and seriously wounded Anne’s chauffeur, her royal protection officer, another policeman and a journalist who came to Anne’s aid. The Princess Royal herself displayed characteristic cool when she refused Ball’s demand to leave the car with the retort ‘Not bloody likely!’ Ball is still detained in Broadmoor hospital for the criminally insane nearly half a century later, after pleading guilty to attempted murder and kidnapping charges.

And Queen Victoria, in her long reign, saw no fewer than eight attempts on her life – including three occasions when pistols were fired at her from close range (but missed), and another attempt when she was battered with an iron tipped cane, leaving her with a black eye.

European royals were much less lucky. In 1898 the eccentric Austrian Empress Elisabeth ‘Sissi’ – the subject of the current movie biopic Corsage – was fatally stabbed by an Italian anarchist as she boarded a ferry on Lake Geneva. Elisabeth was travelling incognito and without protection when she was attacked.

Two years later, in 1900, another anarchist assassinated King Umberto I of Italy at Monza. In 1908, Republican revolutionaries shot and killed both King Carlos I of Portugal and his son and heir Prince Luis Felipe as they drove through Lisbon. Both Umberto and the Portuguese royals were riding in open carriages when they died. In 1913, King George I of Greece was shot dead by a lone gunman as he strolled unprotected through Thessaloniki on his afternoon constitutional.

One of the most infamous royal assassinations took place in 1914, when the heir to the Austrian throne, Archduke Franz Ferdinand, and his wife Sophie were shot dead in their car by Serb nationalist Gavrilo Princip as they drove through the Bosnian capital, Sarajevo. The assassination led directly to the first world war and the collapse of monarchies in Russia, Austria-Hungary and Germany.

The inter-war period saw no let-up in the death toll of Europe’s monarchs. In 1934, King Alexander of Yugoslavia was shot dead in an open-top car – along with the French foreign minister, Louis Barthou – in Marseilles after arriving on a state visit to France. The assassin, who was beaten to death on the spot, was a professional hitman in the pay of Croatian fascists. Alexander’s killing was the first assassination to be captured on newsreel film.

Back in Britain in 1936, during Edward VIII’s brief reign, the new king escaped unharmed in an incident (which remains, to this day, mysterious) when a malcontent named George McMahon threw a loaded pistol at him as he rode on horseback through Hyde Park during a Trooping the Colour ceremony.

What this long litany of near misses and successful hits shows is that kings and queens – simply by virtue of the positions they were born to – are constant moving targets for assassins motivated by malice, madness or misplaced political ideology. In Britain, where the monarchy is increasingly open and informal, King Charles will not want to withdraw behind high walls and heavy security screens. But unless he does so, he and his family will remain vulnerable to someone armed with an item more lethal than an egg.