Standing all alone in a corner of Embankment Gardens, overshadowed by the huge complex which now juts out at the back of Charing Cross station, stands a venerable old water gate. Built in the early 17th century by the great architect Inigo Jones, it is a stylish and imposing edifice which allowed the Dukes of Buckingham access to their private boat.

'But hang on a minute,' as Watson might say to Holmes. 'You called it a water gate. Where on earth is the water? The Thames is more than a hundred yards away'

'Ah yes, my dear Dr Watson,' Holmes might reply. 'But you are overlooking one crucial fact. The Thames was not always a hundred yards away. It has, in fact, moved.' At this point Dr Watson's brains may addle completely and Holmes will launch into historical explanation.

For centuries, Old Father Thames was a much wider and more sluggish river than today's comparatively svelte and pacy waterway. His very bulk meant that a severe winter caused the water to freeze over, much to the delight of Londoners who would hold an impromptu 'Frost Fair' on the ice.

These fairs took place about once every 50 years and Londoners knew how to make the most of them. Stalls would be put up, temporary drinking booths were installed and houses of ill-repute rapidly appeared, offering clients a once- in-a-lifetime experience.

The fatal error for these go-getting entrepreneurs was to ignore the onset of warmer weather and the thaw of the river. The foolish and the greedy would be swept down the Thames on blocks of ice before finding a watery grave in the North Sea.

Londoners also used to deposit their muck and rubbish in the river. By the middle of the 19th century the Thames was little more than foul-smelling sludge. The hot summer of 1858 produced so many noxious pongs that it was dubbed 'The Year of the Great Stink'.

Something had to be done and, with typical Victorian energy, it was. Sir Joseph Bazalgette was commissioned to build a network of underground sewers to prevent the refuse from

reaching the river. He reclaimed 37 acres from the Thames, reducing its size considerably and making the river flow with much greater vigour - which meant, sadly, no more Frost Fairs.

Today, the ceaseless search for profit would have seen huge office blocks erected on the reclaimed land.

The Victorians, fully aware of the value of public space, knew better. The land was turned into the charming and attractive Embankment Gardens.

'Which is why, my dear Watson,' Sherlock Holmes would doubtlessly conclude, 'this water gate has no water.'

The Water Gate is in the western corner of Embankment Gardens, just at the end of Buckingham Street.

(Photograph omitted)