We have to go to the Planetarium to make sure that the stars are all there and then to Madame Tussaud’s to see which stars aren’t, having been carted off in the tumbrel since our last visit. We call in at the Natural History Museum to confirm that the dinosaur is as big as it ever was and at the British Museum to ensure that the complement of mummies is all present and correct. We’d be shirking our responsibilities if we neglected Big Ben, the Tower, Westminster Abbey, Downing Street, Horse Guards Parade and the pigeons in Trafalgar Square.

Like dutiful Alices, my wife and I usher our sons across the Mall to join the crowds outside the Palace, eternally hanging on in the hope that something vaguely interesting might happen. It’s odd, we reflect, how the guards seem to be younger every time we visit, and shudder when we realise that our sons are almost as old certainly too old to use as an excuse for this annual foot-slog along the tourist trail. Of course, they know it too, but don’t make a fuss this London jaunt is, as far as they’re concerned, a treat they are giving us.

Part of the ritual, always, is to resolve to eat somewhere we’ve never tried before, and then always to end up eating at Pollo, in Old Compton Street. It’s cheap, noisy and always packed with an unlikely assortment of tourists, students, Soho types, and courting couples yelling their sweet nothings above the din.

When you’re up from the sticks, that’s exactly what you’ve come to London for to rub shoulders (and indeed, in the crowded Pollo, everything else as well) with all sorts. It’s a Noah’s Ark where disparate species have arrived at a tacit, if temporary, understanding that they must live and let live. “Boys, ” I find myself saying over the second bottle of Valpolicella, “London is the one place where you can genuinely choose to be whoever you want to be.”

They cringe as they can see mum and dad are choosing to be Darby and Joan. Our fingers are arthritic after a day clutching a Harrods carrier bag (compulsory for visitors) and the A-Z (highly advisable). But courageously we reach out to touch across the Formica, aware that we’re heading inexorably towards London’s biggest attraction the dewy-eyed trip down Memory Lane. “Remember when the pushchair got stuck in the lift at Goodge Street . . . when we lost them in Derry and Toms . . . the time he was sick in the Whispering Gallery?” If you come to London without any memories of your own, don’t worry, you can share everybody else’s. There is a collective nostalgia that lingers in the London air as palpably as the exhaust fumes.

Whatever age you are, and whatever corner of the country you’ve spent your life in, you’ll soon find yourself telling your children authoritatively all about the London that was: the Swinging Sixties, the Coronation, the Blitz. You’ll tell them about the days when the streets weren’t paved with McDonald’s wrappers, when there were debs in coffee ‘ouses, Teds in drainpipe trousis, gents with bowler hats and furled umbrellas, chirpy Cockney sparrers, sparkly pearly queens, bobbies on bicycles two-by-two, a morning chorus of street traders, just like in Oliver. And, hand on heart, you’ll tell them how you once heard a nightingale sing in Berkeley Square.

Somewhere in that peasouper of temps perdu you’ll also find almost everything you half-recall from your history lessons this is quite simply the place where anything of momentous consequence happened. The rest of the country might contain a sparse scattering of footnotes, but London is the definitive text. The temptation is to flick through it too quickly with the result that you can easily end up spending your time not in London, but in the grubby nowhere of the Underground.

The buses serve you better if you don’t mind not knowing where you’re going or when to get off when you get there. On board an open-top tourist bus you’re saved that problem, but the guides machine-gun you with so many facts that you feel you’re being crammed for an exam you never asked to sit. No, if you want to feel you’re in the real London, choose the mode of transport that the town has relied upon down the ages and spend a lazy day on the Thames.

Cruisers from London Bridge and Westminster will take you as far upstream as Hampton Court. The moment you disembark here, you experience that unmistakable thrill of stepping back in time. When Wolsey had it built in 1514, he was simultaneously bishop of five sees, Archbishop of Canterbury, Abbot of St Albans, a cardinal, Grand Almoner and Lord Chancellor of England: in effect, he ruled the country on Henry VIII’s behalf, a sort of Michael Heseltine but not so powerful, of course.

The opulence of Hampton Court was Wolsey’s way of demonstrating just how important he’d become, but in fact it proved to be a gargantuan faux pas. It impressed Henry so much that he insisted, as only kings can, on being given it as a present and so it became the out-of-town home of successive British monarchs until Victoria’s day. And despite the millions of visitors who flock here, it still retains the ambience of a real home. Queen Anne’s brushes, combs and suchlike are laid out in her boudoir so naturally it wouldn’t strike you as odd if she were to stride imperiously through the door.

You can wander through the vast Tudor kitchens, handle the utensils and see frozen like the figures on Keats’s urn the slaughtered stag and strangled swan eternally awaiting their turn on the spit. You can visit the private church or see “the great house of easement” where kings and queens had their royal wees. Then there are the grounds: the famous maze (easy-peasy); the tennis courts; the recently re-landscaped Privy Garden, and the acres of rolling lawns and shady trees under which you plan what you’d build should you ever acquire a few bishoprics.

The trip back to town on the Thames is one of the great journeys: perhaps Earth has things to show more fair but it still seems an awesome privilege to be able to sit on deck watching London slowly revealing itself. This is the town as it should be no queues, no elbows, no relentless roar of traffic. You simply let it chug-chug past with the scullers and the swans and those flotillas of little boats crewed by people who know that there’s still nothing as nice as messing about on the river.

You’ll see the jetty at Kingston (where three men set off in a boat); Richmond Park; Kew Gardens; Chiswick Bridge and Putney Bridge; the new Chelsea Harbour development and the wonderfully incongruous Battersea Peace Pagoda. Slowly, you’re aware that you’re in real London as you glide past the Battersea Power Station (gloomily derelict), the Tate Gallery, the Houses of Parliament (which never seem nearly as impressive as they look on News at Ten), the Royal Festival Hall and, eventually, St Paul’s and Tower Bridge.

From here you can take another launch to Greenwich past the surreal excess of the Docklands development where you’ll see architecture you’d have thought only the artists at Marvel Comics could have concocted and only Disney’s Imagineers would have dared to build. I don’t suppose it’s any more outrageous than Hampton Court was in its day. Nonetheless, it’s hard to imagine Charles III ever insisting that he be given Canary Wharf as a present. It’s on to Greenwich, where my family go through the ritual of checking that the Cutty Sark is still shipshape, and that no one has tampered with the Meridian Line at the Observatory since we last stood astride it.

Then the final leg of our journey which takes us to the Thames Barrier that colossal high-tech promise that the Noah’s Ark which is London need never again fear the rising of the waters. I confess that, despite the educational videos and instructive leaflets, I can never quite figure out how it’s supposed to work. That doesn’t stop me, of course, from giving it the most rigorous inspection. After all, as an absentee landlord, I might not want actually to live in London (there are too many tourists with Harrods bags for my liking), but I want to be sure that it’s always going to be there for me.