Changing the rules

Whom might the great queen Margaret Tudor's eye fall on next as her sixth potential husband? In her desperate quest to have a female heir to keep the succession secure, she would stop at nothing. Fantasy? Of course. For Margaret Tudor, Henry VIII's older sister, did not inherit the English throne ahead of him but was packed off to marry James IV of Scotland (embarking on some hair-raising love affairs there).

But, as British Prime Minister David Cameron announces plans to consult the Commonwealth about reforming the succession - meaning that any daughter born to the Duke and Duchess of Cambridge could inherit the throne above a younger brother - it provides a tantalising game of ''what might have been'' if the laws of precedence had been altered earlier. For which great female monarchs have we potentially missed out on - and which very disreputable kings could we have avoided?

Could we have missed major events, such as the First World War, if a princess royal rather than a prince of Wales had been permitted to be heir to the throne? Women monarchs got off to a slow start in England. ''We've never had Salic law [which allows no female inheritance at all], so it has never been impossible for a woman to inherit,'' the historian and author of The Girl in the Mirror, Sarah Gristwood, says.

''But in medieval times, the king led the army and women were considered subject to their husbands,'' Gristwood says. ''Powerful religious authorities ruled that women were completely inferior to men, ruling out their chances of running the country.''

This wasn't helped by an early experiment in female rule: in 1135, the Empress Matilda was named heir to her father, Henry I, and ushered in a 19-year power struggle with her cousin, Stephen, called ''the Anarchy'', in which it was said ''Christ and his saints slept''. Lukewarm enthusiasm for women rulers was thus set back hundreds of years, until the Tudors managed three female monarchs in the space of half a century (Lady Jane Grey, Mary I and Elizabeth I).

Historian Alison Weir makes it clear, however, that the Tudors should never have been Henry VII's dynasty. Indeed, he had a lesser claim to the throne than his own mother, Lady Margaret Beaufort. ''She never asserted her right,'' says Weir, author of Mary Boleyn: The Mistress of Kings.

''Everything was invested in her son. But she'd have made an incredible sovereign - she was a political operator behind the scenes, wily and devious, overshadowing Henry's own wife. She later signed herself Margaret R - which could stand for Margaret Richmond [the surname of her fourth husband] but certainly sounds suspiciously regal.''

Meanwhile, if the laws of precedence had been altered, Henry VIII would have come second in line to his older sister Margaret, although, Weir adds, ''she would have been a disaster. She completely let her heart rule her head when it came to matrimonial adventures.''

Henry daughter, Elizabeth, transformed the notion that women could not be monarchs.

''I think she is our most impressive ruler. She regularly leads polls of the top monarch of all time,'' Gristwood says. ''And she used her gender as a strength rather than a weakness. She showed the qualities of queenship could include flexibility; she took a country that was a small player in Europe, at a time of religious controversy, and performed a remarkable juggling act.''

While kingship may have been defined by leading an army, another of the qualities of queenship is longevity - with Elizabeth I, Victoria and our current Queen notching up more than 160 years between them.

Yet other female monarchs with shorter reigns should not be dismissed.

''Mary II is often forgotten but she's pretty terrific. She invades Britain with her husband William and knocks her father [James II] off the throne and ensures Protestantism survives,'' the chief curator at the Historic Royal Palaces, Lucy Worsley, says.

''Both she and her younger sister, Anne, fail in their duty to reproduce but they achieve a smooth transfer of power, which shouldn't be underestimated.'' The death of both Mary and Anne brought in the 1701 Act of Settlement, which enshrined male primogeniture in law. Worsley points out that this meant not only was Princess Augusta, elder sister of George III, barred from being queen, but Britain also got saddled with George IV.

''We don't known much about Augusta, but her daughter, Caroline, was very feisty,'' Worsley says.

''And if [Augusta] had inherited, at least then we'd have missed out on George IV, which would have been no bad thing with his drinking and drug-taking.''

However, at least, Worsley adds, the country always stopped short of imposing Salic law, which could have led to an even worse ruler.

''Salic law meant Queen Victoria could not inherit the Hanoverian lands in Germany, which went to her uncle, the Duke of Cumberland - a rather dodgy manwho killed his valet in mysterious circumstances.''

But what important events could also have been avoided by allowing women to inherit? It's hard not to wonder what would have happened if Elizabeth Stuart had become queen, rather than the younger Charles I, whose ineptitude saw the country spiral into the English Civil War.

''I think Queen Victoria's daughter, the Princess Royal (also called Victoria), had what it takes to be a great queen,'' Weir says. ''Unfortunately, she was sent off to the Prussian court to be married ... Yet, I think she could have been the ideal constitutional monarch - she had great integrity, an instinctive feel for what was right, a commanding presence and greathumanity.''

But, crucially, had she become Queen of England, would Princess Vicky have ever married Frederick William of Prussia and become mother to Kaiser Wilhelm II, the ruler whose policies helped spark the First World War? ''A marriage like that to a foreign prince would have caused so many factions, I'm not sure it could have been allowed,'' Weir says. ''It's one of the great 'what ifs' of history.''

London Daily Telegraph