They could cruise through the Mediterranean, calling at Gibraltar, Malta, Cyprus and Palestine. They could sail south through the Suez Canal, stopping at Port Sudan or Aden, and continue down to east Africa, or across to India. Beyond here, they could meander their way through Burma, Malaya, Singapore and Hong Kong, before heading into the Pacific.
The imminent hand-over of Hong Kong back to China is often referred to, with a degree of melancholy, as the "End of Empire". Certainly, Hong Kong is the last of the major world ports which British cruise ships could call their own. But does this really mean that British tourists must now fend for themselves once they leave the English Channel?
Not quite. Those nervous travellers who can't bear the idea of losing the protection of the Foreign Office will still have a few options overseas. Well into the next century there will be vestiges of empire where you can drink afternoon tea, drive on the left and witness beplumed governors celebrating the Queen's birthday.
These corners which will be forever England (no longer colonies but "British Dependent Territories") may be small and economically insignificant, and largely concentrated in the Atlantic Ocean, but it is still just about possible to hypothesise a round-the-world cruise, calling at British territory only.
The first port of call out of Southampton will be Gibraltar, which, with its apes and rocky profile is set to become Britain's best loved possession after the loss of Hong Kong. Empire nostalgics needn't worry, by the way, about Britain losing the Rock any time soon - and certainly not before Spain relinquishes its colonies in Morocco.
From Gibraltar, heading a couple of thousand miles due west will bring the cruise to Britain's soon-to-be most populous and wealthy territory, Bermuda. This may be culturally a part of the United States, but it has been British for three hundred years.
Further south, in the Caribbean itself, our hypothetical cruise goes into overdrive. You'll still find the Union Jack being lowered at dusk here in the Cayman Islands, the British Virgin Islands, the Turks & Caicos Islands, Montserrat and Anguilla. And jolly delightful little places they all are, with superb diving and swimming. For the record, the Caymans, in addition, are blessed with more than US$500bn worth of banks.
Moving on from here, our cruise takes us below the equator to another area rich in British islands, the south Atlantic. A string of territories - Ascension, St Helena, Tristan da Cunha, South Georgia and the Falkland Islands - provide stepping stones all the way from the tropics to the icy waters of the far south. Finally, for hardcore flag fanatics, is British Antarctic Territory, which, at over 600,000 square miles, remains by far the largest of all the dependent territories.
Once around Cape Horn and into the Pacific, however, the British Empire becomes very thin indeed. Minuscule Pitcairn Island, inhabited mainly by the culturally isolated descendents of Bounty mutineer Fletcher Christian, lies some four thousand miles northwest of the Horn. Further west still lies an even greater wilderness, a gaping hole left by the disappearance of Hong Kong.
Discounting Fiji and Australia, both of which retain the Queen on their money, some ten thousand miles - perhaps thirty days at sea - separate Pitcairn from Britain's next flag-pole, on Diego Garcia in the British Indian Ocean Territory. And even this is uninhabited, except by the military.
And that is the whole story. From Diego Garcia back to Gibraltar, via the (Egyptian) Suez Canal is another six thousand miles. Six thousand miles without a home-brewed British cup of tea? The British Empire has certainly seen better days. But it is not quite dead yet.