News of the birth is unlikely to be posted on the main gate at Buckingham Palace, although given Mr Blair's presidential style some cynics might think nothing should be ruled out at this stage.
In any event we may be sure that Her Majesty Queen Elizabeth will lead the nation in congratulation and celebration, come the hoped-for safe arrival of Tony and Cheri's fourth child next May. And since the House of Windsor will have no comparable event with which to entrance and uplift the country - certainly not before the arrival of Prince William's own son and heir, presumably well into the new millennium - the first Downing Street birth in 152 years will unquestionably command all the press and media enthusiasm traditionally reserved for royalty.
Mr and Mrs Blair have in fact been diligent, and fairly successful, in their efforts to spare their children the media spotlight. However, if the headlines greeting news of Cheri's unexpected pregnancy back in November are anything to go by, the prime minister and his wife will have difficulty keeping their little bundle of joy under wraps.
Cynicism aside (well, briefly at any rate) - genuine and widespread pleasure greeted Mr Blair's astonishment upon learning that something other than Northern Ireland might be the cause of his future sleepless nights. The image of Tony and Cheri with their three children on the steps of Number 10 that sunny afternoon in May 1997 proved one of the most enduring of New Labour's triumph - and, for many people, one of the clearest illustrations of their break with a Tory Party believed to have grown rotten and corrupt through too many years in power.
For many - but not, of course, for all. New Labour had already come to be seen by others as a permanent triumph of style and presentation over substance. And Mr Blair's image makers could hardly have been unaware of the centrality of Mr Blair's strong family life, as they tailored their package for a middle England grown disillusioned with the Conservatives as the party of traditional values.
Small wonder, then, cynics should be on hand to marvel that news of the pregnancy should leak in the middle of the shambolic, and ultimately doomed, leadership attempt to keep Red Ken Livingstone out of the race to become Labour's candidate for London Mayor.
Or to observe that the happy event might mercifully coincide with the London election itself - so eclipsing Mr Livingstone a second time should he (horror of horrors) beat Frank Dobson and Glenda Jackson to claim the nomination in February and the Mayoralty itself come May.
For once Alistair Campbell, the Prime Minister's official spokesman, known to some as the real deputy prime minister, was in line neither for congratulation or blame. But the ebullient Mr Campbell - while rubbishing any suggestion of media management - will have been chortling at the memory of Harold Macmillan's "events", and marvelling at their capacity for political good as well as for ill.
Certainly he will have enjoyed the waspish conclusions that not even an announcement of twins for William and Ffion would now be enough to put the Conservatives back in contention come the next election. And the Downing Street and Millbank strategists will have sighed with relief when the public rewarded the evidence of prime ministerial virility by reversing a worrying tendency which had one poll cutting Labour's lead to just ten points.
In an instant, it seemed, months of hard endeavour by the Tory leader had come undone. The memories of that victory in the European elections in June (the Conservatives' first national win since the local elections in June 1992); a relatively successful party conference; and the mauling of Mr Blair over the Queen's Speech were erased as the nation basked in New Labour's familial glow.
As if news of the expected Blair babe was not bad enough, Lord Archer completed the double-whammy - dramatically resigning as Tory candidate for London Mayor amid fresh allegations that he had lied, and been prepared to pervert the course of justice, in respect of that celebrated libel case 12 years before.
Against the backdrop of the Neil Hamilton/Al Fayed court action - and a gathering controversy about the Tory party treasurer Michael Ashcroft and the party's rules on foreign funding - allegations and suggestions of Tory sleaze were back in the headlines. So too were questions about Mr Hague's leadership, and just as Michael Portillo returned to the Commons courtesy of the Kensington and Chelsea by-election.
Westminster wisdom has it that there will be no leadership putsch in the coming year, and that Mr Portillo will play the loyalist card. However there is little comfort for Mr Hague in that certain expectation. For the equally certain belief is that Mr Portillo would not want to lead a party heading into a second general defeat. Indeed, as Mr Portillo prepares for an inevitable return to a distinctly under-whelming Tory front bench, the keenest speculation is whether he can successfully resist the offer of the party chairmanship - and so avoid being too closely associated with near-inevitable failure.
Such at any rate was the prevailing mood of despair inside Conservative Central Office as the year drew too a close and the London selection panel axed former transport minister Steve Norris - so giving the party a choice of four unknowns and every prospect, as one insider put it, of trailing third in the Mayoral race behind the Liberal Democrats.
Mr Hague, too, must ever-more-desperately pin his hopes on events. In the past 12 months there have been events enough to warn Mr Blair against taking the British public for granted.
Toward year-end Mr Blair found himself in a thoroughly Thatcherite position - isolated at the heart of Europe, forced to do battle for the British interest over beef and taxation, knowing all-the-while that confrontations with his would-be allies only reinforce continuing British hostility to membership of the Euro. Earlier in the year voters in Scotland and Wales denied Labour overall majorities in the Scottish Parliament and the Welsh Assembly - forcing Alun Michael to form a minority administration in Cardiff, and Donald Dewar to negotiate a full-blooded coalition with the Liberal Democrats at Holyrood.
Mr Blair's programme of constitutional reform has had a relatively inauspicious beginning, and there is still unresolved the glaring tension between the Prime Minister's desire to devolve and his instinct to control. Nowhere is that tension more publicly on display than in London.
Frank Millar can be contacted at fmillar@irish-times.ie