The penthouse, in short, is the architectural expression of unsurpassable success: in terrestrial - not to mention residential - terms this is as definitely as high as you can go. Literally, and symbolically, you've reached the top. Next stop, presumably, is Nirvana.

We now take all of these aspirational associations for granted but in truth the penthouse owes more to the invention of the safety elevator than it does to the demands of the seriously wealthy for a premium perch. 

Before the invention of the lift, the penthouse really was "a structure or dwelling built on the roof of a tall building". A fairly humble structure at that: it was a long slow climb to the top, so roofs were kept for laundry houses, washing lines, water towers, servants' quarters and the like. 

The first were in America - in high-rise Chicago and New York. In 1925, Marjorie Merriweather Post Hutton commissioned a spectacular 54-room triplex apartment on top of a 14-floor building on Fifth Avenue, New York. 

It had a silver room, a wine room, a cold storage room for furs and flowers, and lavish suites of rooms. A private lift ran down to the ground floor, where a concierge was on hand: a new residential form had been born.

Until quite recently London was not the first, or even the second choice, for your serious penthouse devotee. If you wanted a city apartment with a commanding view Manhattan had plenty to offer but London came up rather short.

Peter Walker, who works for PR company TTA, which has many of the UK's top developers on its books, reckons these are heady days for the penthouse here. "In the past, the thought and attention hasn't really gone into them here as much as in the US, but that's changing.

There's a move towards high-rise development in London and developers have started to make a serious effort with the penthouse. Ballymore are a good example. They worked with a top American architect - Skidmore Owings & Merrill - to create New Providence Wharf, which has some of the most remarkable penthouses in London."

At New Providence the penthouses came with 3,000 sq ft of internal space and up to 3,700 sq ft of terracing complete with saunas, grass gardens, and the real showstopper, private heated swimming pools.

"With penthouses, says Peter, "they don't sell off plan - they're living spaces and people want to see them and walk around before they part with vast sums. But at New Providence - because they were different and exceptional - they sold five off-plan of the seven."

Ballymore has recently been granted planning permission to build Europe's tallest residential development at 1 Millharbour, in London Docklands - 700 apartments located in two interlinking towers rising to 36 and 50 storeys.

They will, says Peter, be working hard to top their New Providence penthouses, and are already in informal talks with prospective buyers such as Donald Trump.
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"The scheme will offer a range of hotel-style services including valet parking and a 24-hour concierge who will be able to arrange everything from dry cleaning to dinner parties. Work begins in Autumn of 2005 and the development is scheduled for completion in 2009."

But what of those who can't wait that long and don't want to live in Docklands? If penthouse for you means high-rise there's always the Barbican. "There are three penthouses per tower over two or three floors," says Mark Harrison of Frank Harris and Company. "In one tower the penthouse is a triplex laid out of the 37th, 38th, and 39th floors with conservatory at the top. The views are spectacular. St Paul's looks like a village church." Riverside development has also been a major trend in recent years and there are some spectacular developments - notably Richard Roger's Montevetro in Battersea: 20 storeys topped by seriously extravagant penthouses with floor to ceiling glazing that makes the most of the views.

Mansion blocks, the first apartment buildings in the UK, provide luxury living with a degree of period grandeur, while their flat roofs have provided developers with the opportunity to construct prefabricated penthouse pods that sell for millions - Swedish company First Penthouse are the leaders in this particular sector. 

One-off architect designed penthouses have also become a feature of the London market - for one of the most eye-catching check out David Conner's staggering apartment in Primrose Hill.

Redevelopment in prime locations in central London has also resulted in some extravagant upmarket efforts - Peter Walker cites the penthouses by Crown Dilmun in Trevor Square (once part of Harrods) as an excellent example. 

Upmarket design maestros Candy and Candy recently completed a magnificent penthouse in the same development - over 6,000 sq ft of high tech luxury that sold for a cool £14 million.

The redevelopment industry has also led to that peculiar architectural hybrid - the loft penthouse. Lofts may once have been the preserve of bohemian types but they went upmarket a long time ago.

Top floor shell spaces, says Caspar Dixon of Urban Spaces, are the place anyone with the money wants to be: "You're above everyone else, away from the noise and pollution of the streets and the roof can provide a great outside space."

Loft dwellers typically bring in their own designers and architects to fit the place out and this has resulted in some superb bespoke apartments - Bankside lofts, Summer Street lofts and Soho lofts are among the most authentic and sought-after developments.

Penthouses: The Facts 

1. Usually, though not always, the top floor. Great views, terraces, balconies and outside space.

2. Private lift or lift that allows penthouse owner privacy while s/he is using it. 

3. High-tech features such as comfort cooling, plasma screens in bathrooms and bedrooms, touch pad electronic controls, integrated sound system, high-tech lighting and security systems, etc.

4. Top of the range fixtures and fittings: brochures will invariably name-check, Lutron, Bang & Olufsen, Creston, etc. 

5. Exceptional bespoke design and use of highest quality materials - architectural glass, rare timbers, solid oak floors, marble, hand-painted silk wallpaper etc.

6. Saunas, steam rooms, wet rooms, swimming pools, cinemas and media rooms.

7. In developments: top notch concierge services. More recent penthouses crown developments with restaurants and hotel type services.

8. Buyers: rich, and super-rich (celebs, corporate kings etc). 'Boy done good' types - one of the penthouses in New Providence was sold to a scrap metal merchant. International types in search of a bolt-hole with the wow factor.

9. Buyers: in the loft market, arty and design types who want to create their own bespoke space.

More about penthouses: Check out Jonathan Bell's excellent new book Penthouse Living, Wiley 2005.