While the world – and especially the bookies – enjoy the traditional speculation over the sex and name of any impending royal arrival, the future third in line to the throne has already made royal and constitutional history.
For he or she will be the first addition to the new-look, non-sexist line of succession which will govern the Crown for evermore.
In short, the Duke and Duchess of Cambridge’s first-born will trump all subsequent siblings, even if she is a princess who is followed by a string of younger brothers.
Happy couple: Kate and William's baby will be third in line to the throne and has already made royal and constitutional history Enlarge Changes: Last year, David Cameron decided that the time had come to tackle the status quo and change the rules of successionLast year, David Cameron decided that the time had come to tackle the status quo and change the rules of succession.
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It was never going to be straightforward. For any change could even lead to meddling with such fundamental constitutional humdingers as the Act of Union.
And that is not the only reason that Mr Cameron’s predecessors have flinched from doing anything about this.
Other monarchies have already changed their succession laws. In Sweden, famously, the toddler Princess Victoria was suddenly promoted to Crown Princess ahead of her infant brother who had actually been born Crown Prince.
But things have always been more complicated in Britain because the Queen is Sovereign of 15 other countries, from Canada to Tuvalu. Any change had to require simultaneous unanimity from all of them.
Once William had made his marriage vows, however, it was clear that this had the potential to become a more pressing issue.
So, Mr Cameron decided to act while he had the prime ministers of all 16 nations in the room at last year’s Commonwealth summit in Perth. They all signed a ‘heads of agreement’ which means that the new system is now acknowledged and already applies de facto.
However, it still needs to become law (or become de iure, as lawyers like to say). Britain must legislate first so that all the other 15 parliaments can follow suit but Westminster still needs a document of ‘formal consent’ from all 15 individual governments before it can proceed.
So, the pressure is now on two politicians to get on with it.
One is Nick Clegg, the Deputy Prime Minister and the man in charge of the ‘political and constitutional reform agenda’. He will be responsible for steering a new Succession Bill through Westminster.
The other is John Key, the Prime Minister of New Zealand, who has been charged with rounding up all the necessary ‘formal consents’ from the other realms.
Last night, a Cabinet Office spokesman said that no timetable was in place but Mr Clegg already has the necessary Bill drafted and ready for Parliament as soon as Mr Key gives him the go-ahead.
The process is still fraught with political implications.
Under pressure: The Deputy Prime Minister is in charge of the 'political and constitutional reform agenda'MPs with Scottish nationalist or republican leanings may see it as a welcome opportunity to enjoy some political mischief and slap down some awkward amendments.
John Key has been charged with rounding up all the necessary 'formal consents' from the other realmsAmong the peerage, there will, no doubt, be many sisters and daughters of hereditary dukes, marquesses, earls, viscounts and barons who feel that the time has come to amend the inherent sexism in Britain’s aristocracy.
The loudest complaints, however, will come from those who point out that the British laws of succession continue to discriminate on religious grounds because the monarch is barred both from being a Roman Catholic – although the new rules will allow him or her to marry one. It is at that point that ancient legislation like the Act of Union could be examined.
In the past ten years, Tory, Labour and Lib Dem MPs have all attempted to introduce Private Members’ Bills to change this aspect of the succession; the most recent was last year.
It seems likely that some MPs will want, at the very least, to extract a commitment from the Government to end what they regard as all sectarianism at the heart of the British constitution.
Mr Clegg has his work cut out.
The Queen, as ever, will abide by the will of Parliament.
Meanwhile, there are other priorities for the duke and duchess – and the unborn HRH Prince or Princess X of Cambridge. Such as: When are the builders going to finish their new married quarters at Kensington Palace?
