We Brits don't much care for uniformity. Just as well, if you live next to the man with a large shark sticking out of his roof. Adrian Mourby celebrates our love affair with odd buildings, mad customs and home-grown eccentrics

Castle Ward in Downpatrick is an unusual house. One side is neoclassical and the other Gothic. The design was the result of the 18th-century owner and his wife being unable to agree on what style they wanted. Lyveden New Bield in Northamptonshire is also unusual. Its 16th-century builder, Sir Thomas Tresham, was a man obsessed with the number three, so every dimension within the house is its multiple.

Tresham also built the Triangular Lodge in nearby Rushton on similar principles. In Devon, A la Ronde is a 16-sided house decorated with sea shells, constructed by two 18th-century spinsters to display their Grand Tour treasures. At Ickworth in Suffolk the 4th Earl of Bristol built an oval house because this was his favourite shape. And in Penzance stands a convincing Egyptian house with lotus-bud capitals.

The UK probably has more eccentric buildings than any other country, the result of its early affluence fuelling the idiosyncracy of those who could afford to build what they wanted, where they wanted.

Uniformity is something the British have always baulked at. After buildings in Paris were destroyed in 1871, Baron Haussmann replanned the city's centre in one harmonious style, an achievement that eluded Sir Christopher Wren in London in 1666, after the Great Fire, despite splendid plans that would have created a Renaissance city by the Thames. Property laws and British bolshiness defeated him. Even Bath, most coherent of cities, has oddities: Sally Lunn's, Beckford's Tower and Sham Castle.

Individual vision certainly accounts for much eccentric building. In the 19th century, Cardiff's Marquess of Bute revamped two of his properties - Castell Coch and Cardiff Castle - to resemble his vision of a medieval Wales - an exquisite fantasy. But other buildings in Wales - the Ugly House in Capel Curig and Conwy's "Smallest House in Britain" - are as they are out of practicality. The Ugly House was built overnight according to an ancient law that legitimised any building constructed in the dark that had a fire going by sunrise. The Smallest House was simply squeezed in between two others.

Sadly, exuberantly eccentric building seems to have gone out of fashion. Our definition of what is not eccentric has expanded and now takes in houses where floor orders are reversed, public buildings are shaped like gherkins and houses have streams running through them. Look for Eccentric Britain today and you'll find it in private museums, standing as testament to individual obsession, or bizarre activities.

The Gnome Reserve in West Putford, Devon, is a four-acre garden with more than 1,000 gnomes and pixies. Teapot Island in Yalding, Kent, is home to Sue Blazye's collection of nearly 5,000 teapots. Designs include a Dalek, a flying saucer, and Teapot Island itself, a green pot nestling in a sea of blue with a little fishing boat and a tiny gold lid.

"Do I consider myself eccentric? " asks Sue. "No, but other people do. My collection began in 1983 when my grandmother gave me one of her teapots ... Family and friends began to give me teapots, and before I realised it, I was a teapot collector."

When Sue's collection outgrew her house in Sidcup she openedTeapot Island in Yalding - in November 2002. In 2004 her collection made the Guinness World Records book. "Britain has always nurtured the unconventional," she says.

As for eccentric activities, you don't have to look far to find a medieval egg-rolling or cheese-rolling contest. In Wisborough Green, West Sussex, the British Lawnmower Racing Association has been arranging fixtures since 1973. "We needed a cheap motor sport," said Jim Gavin, one of its founders.

In Staintondale in the North York Moors National Park, Bruce Wright runs a llama-trekking centre - simply to make money. "In 1969 I took over the family farm, but politicians and the EEC hit many smaller farmers like myself and we just had to diversify."

But, in building, it takes something extreme these days to qualify as eccentric. Take the Headington Shark. This rooftop installation was commissioned by Bill Heine, owner of No 2 New High Street, Headington, in 1986. For the next six years Oxford City Council tried to get him to remove it on the grounds that a 25ft fibreglass predator was out of context in a small, brick-built 19th-century street.

Heine countered that it was there to commemorate the 41st anniversary of Hiroshima. In the end the office of Michael Heseltine, Secretary of State for the Environment, ruled: "Into this archetypal urban setting crashes (almost literally) the shark. The contrast is deliberate ... [but] an incongruous object can become accepted as a landmark after a time, becoming well known, even well loved in the process."

Plenty of people visit the Headington Shark, just as they visit the Triangular Lodge and A La Ronde. The Heseltine verdict might be said to define British eccentricity, "an incongruous object can become accepted as a landmark ... becoming well known, even well loved in the process".

Yes, there is life in eccentric Britain yet.