But well before Britannia and its cargo of notables lose sight of shore, the historians will have begun their work. Could Britain have secured a better deal - indeed, did it really have to come to this? In fact, our record on Hong Kong is mixed. British dominion has entrenched the rule of law. Its tutelage may not have directly brought about the economic miracle that is modern Hong Kong, but has provided a stable framework for it. And, despite rancour over the final details, the handover itself is planned and peaceful, which is more than can be said for some previous disposals of empire.
But the blemishes are no less; among them Britain's long indifference to, and ignorance of, the country with which it would have to resolve Hong Kong's future. Most glaring, however, was the failure to introduce democratic institutions sooner. The reforms sponsored by Chris Patten were an entirely reasonable response to the horror of Tiananmen Square in 1989 - but they were not provided for in the Joint Declaration five years earlier, which set the terms of today's transfer of sovereignty. China therefore can justify the abolition of the elected legislature, and its replacement by a hand-picked assembly, with the argument that the former was no part of the agreement signed by Mrs Thatcher.
So much for the past. What matters is not the high pomp and low circumstances of these 50 celebrity-strewn hours leading up to the handover but the next 50 days, 50 months, and the 50 years Hong Kong is theoretically to retain its separate system. And Britain's hand is weak - to reverse Stanley Baldwin's remark about the press barons, we are in a position of responsibility without power. Our duty is to do all that we can to safeguard Hong Kong's prosperity, and to use what influence we retain to protect the new liberties of its people. The first, one suspects, will take care of itself. The second will be far harder.
If recent events have shown Britain has had little ability to carve Hong Kong's destiny in stone during these last years of colonial rule, in future it will have even less. The simple truth is that China can do whatever it wants in Hong Kong. If it chose to send in not 4,000, but half a million People's Liberation Army troops tomorrow, or to jail Martin Lee and every member of the Democrats party, neither Britain nor that genuine Pacific power, the US, could do anything to stop it. To suggest otherwise, to seek to protect democracy with grandiloquent promises that cannot be met, is merely to invite humiliation, and charges of betrayal from those who took the pledges at face value.
This is not to overlook China's blatant shortcomings on human rights, still less to justify them as part of a remote and incomprehensible "Asian culture" - all in the interests of not upsetting a market for British exports which embraces a fifth of the world's population. With or without Hong Kong, the relations between the West and Asia's emerging superpower will always be prickly. Britain and its allies must scold China where necessary, call it to account before international bodies, and exert the maximum pressure to keep Hong Kong squarely in the international spotlight. If only every annual meeting of the IMF could be held there, not just the one coming up this autumn.
For Britain in particular, any notion of a "choice" between China and Hong Kong is a nonsense. British investments in Hong Kong are three times as great as in the rest of China, and Lord Palmerston's "barren rock" is now the seventh greatest trading power on earth. For British diplomacy, Hong Kong and China are perforce a single subject. A smooth transition and an honouring of commitments will vastly improve relations between London and Peking, and give us an inside track into the Chinese market that France, Germany and the rest can but dream of. The reverse will sour ties across the board.
In the end, democratic freedoms will survive in Hong Kong only to the extent that Peking perceives them to be in its own national interest. Economic calculations would argue for restraint and tolerance by China. But the political sums are another matter. The vast skein of personal and economic ties woven between Hong Kong and the rest of the world should give the Chinese leadership pause for thought; but Tiananmen Square was proof, if any were needed, of the profound and eternal aversion of China's gerontocracy to all things pluralistic and democratic. The West's cherished belief is that, wherever applied, its liberal economic system will lead inevitably to political freedom, too. But for Peking, that is all the more reason to impose on Hong Kong either strict quarantine, or ruthless medicine, to prevent the democratic virus spreading north.
So we must wait and watch. Far more than the provisional legislature, whose inauguration ceremony tomorrow has generated such diplomatic heat, the acid test of China's intentions will be the fulfilment or otherwise of its promise to hold elections for a new assembly within 12 months. In fact, there is absolutely no reason why this vote should not be held far sooner. If that deadline is not met, then forebodings about the fate of democracy will be justified. For Hong Kong and its six million people, the date that matters now is not today, whose ceremonial place in history is assured, but 30 June 1998.