It's the dip that makes the trip for Duck tours

Do those ramshackle-looking yellow tour buses you see lurching round central London really motor down the Thames with a crew of slightly scared children aboard? Hard to believe in an age of health and safety panic that this is possible, but it is. And it all happens very quickly, down a slipway you've never noticed next to the MI6 building in Vauxhall. Within moments of turning off the Albert Embankment towards the murky windswept water, London Duck Tours' yellow amphibious vehicles are in it. The deep wet stuff is only a couple of feet below the edge of the open windows of the bus.

Veering about below the terrace of the House of Lords was exhilarating, especially when another boat came surprisingly close; even our rather aloof 14-year-old French exchange student seemed impressed.

Most of the tour, however, is the standard issue drive around Parliament Square, up Whitehall, through Trafalgar Square, along Piccadilly and past Buckingham Palace, all compulsory viewing for those who have not done it before, but not ideal for those who have. The tour guide does his best but the open sides of the vehicle make it quite hard to hear the commentary above the traffic noise.

The sheer surprise of descending onto the river, pottering down from Vauxhall towards Westminster at a respectable speed and emerging smoothly again onto the slipway, is what makes it all worthwhile. The bus did its impression of a horse, cheekily discharging copious amounts of water as though trying to rust the fortifications of the MI6 building, then returning to the road for the journey home, past Lambeth Palace and a glimpse of the Archbishop's enormous garden marquee.

The operator could do more to explain to mechanically-minded kids just how this vehicle, a descendant of D-Day landing craft, operates with both propeller and wheels. However, the watery part of the trip should be just the thing to tempt even hard-to-please London children into visiting the capital's must-see sights.

London Duck Tours run halfhourly, seven days a week, 10am to 5.30pm, starting and ending in Chicheley Street, Waterloo, SE1, close to the London Eye. The 75-minute tour costs £19 for adults, £13 for under-12s, £15 for OAPs and 12-16-year-olds, with family tickets at £57.50. www.londonducktours.co.uk. 020 7928 3132