London wears many masks. It has been called a city of tribes . It grew from villages surrounding a Roman fort into one of the planet's first mega-cities. It is multi- everything . It is historic and it is broad.

You can 'Prime Minister watch' at Downing Street, go Queen spotting at Buckingham Palace, try to avoid pigeons in Trafalgar Square or stroll through the Royal parks. This is the tourism of postcards and plastic gifts, where a can of lukewarm Coke costs a quid (that's £1, or about $1.65).

But, we're looking for 'gritty London' - the bits you can just about see from the top floors of the Hilton, in Park Lane but would not venture into. Areas characterised by ethnic diversity, affordable bars, colourful markets and cracked pavements. Our London is the run-down boroughs of places like Hackney, Lambeth and Tower Hamlets where two-fifths of the city's population lives.

It may be a bit ragged and run down but its broken-toothed smile is genuine.

Not to say that being a bit down-at-heel makes these places particularly cheap. You may be able to sit down for a filling and pleasant 'all-the-trimmings' kebab for under a fiver (that's £5, or about $8.25) at the warm and hospitable Halkevi Kurdish restaurant in Stoke Newington (north-bound 149 bus from Liverpool Street station) but you'll be paying eighty quid a week (about $132) for a room in a smelly, shared flat above the place.

With the possible exception of Moscow's giant 'anything goes' flea-markets, there is no city quite like London when it comes to cheaply-priced markets which line its high streets, fill its church halls and occupy its vacant parking lots.

Ranking the city's multitude of 'free-market institutions' in any kind of order would deny them their uniqueness but if eccentricity is what you are looking for then Hackney Dogs' Car Boot Sale (Hackney Wick train station, Silverlink Train eastbound from Richmond), religiously held every Sunday morning, takes the biscuit. There are more characters here than you'll find crammed into your average Dickens novel. With temporary stalls erected wherever there's space, everything and anything is up for grabs. "Ask me no questions and I'll tell you no lies" goes the sales patter - as long as you can pay in cash.

With nearly one in three of inner London's 2.7m inhabitants describing themselves as non-white many markets are a comfortable reminder how multicultural this metropolis really is. Ridley Road market (Dalston Kingsland station, Silverlink Train, eastbound from Richmond) caters to its largely Caribbean, West African, Southern Asian and Turkish consumer base with stalls selling plantain, salt-fish, oxtail, stuffed green olives and fresh coriander in one of the city's most amazing Saturday morning melting pots. Ridley 24-hour Beigel (or 'bagel' to you) Bakery serves up strong tea and colourful Jewish fare from its no-nonsense corner shop location.

Church Street (also served by the superb and old-style 73 bus) is north east London's gentrification 'frontline' with inviting pubs and well-priced restaurants pushing their way further and further into the hinterlands of 'untrendified' Clapton and beyond. In the day it is an affable part of town where moderately ostentacious wealth is tolerated but at night - like most of London - its personality changes a little. It's never threatening but it's always edgy.

If London's East End were a mental condition it would be multiple personality syndrome. Brick Lane Market (Liverpool Street Station, Central, Circle and District tube lines) is where the symptoms are most acute. Young Bangladeshi entrepreneurs selling mobile phone accessories share stall space with white East London 'geezers' knocking out sea-food spreads of cockles and mussels. Another 24-hour beigel bakery belts out familiar cuisine. On Bacon Street gangs of elderly men in long coats 'flash' curious buyers with the linings of their jackets - 'gold' watches ("nah, 'onest mate, not stolen - straight up"), pens and cuff-links dangle from the insides of their mobile 'shops'. Nearby long-established trader families operating out of trailer units sell everything from meat to stereos at prices that plummet with the speed of the Yugoslavian dinar - "I ain't asking seventy - even fifty would be unfair and, 'cause I'm good-hearted, it ain't even gonna' be forty. I want thirty pound for the pair!" shouts a man through a microphone as he holds two mock-Victorian lamps above his head.

There are a number of other markets nearby - also held on a Sunday - including the famous Petticoat Lane and Spitalfields (both served by Liverpool Street Station) but it's colour, culture and charisma we seek and without fail the fruit and veg market in Brixton (the heart of black Britain) rules the roost. Granville Arcade, Electric Avenue (made famous by reggae artist Eddy Grant), Atlantic Road and a maze of little side streets and alleyways keep the life blood flowing through this part of south London (Brixton Tube, Victoria line) where cost-cutting stalls punt out fresh produce, second-hand books, clothes, army-surplus gear and jewellery.

Brixton, like Brick Lane, is changing into a 'trendy' area. Its rapid rise from economically-deprived 'tough as boots' ghetto into trend-setting bohemia is a relatively new phenomenon. With house prices in the capital sky-rocketing it is a trend affecting London's entire inner city belt: rough areas with access to a tube line are suddenly catapulted into the status of chic des-res; fish and chip shop one moment, sushi bar the next.

If Brixton provides an example of an area in the throes of gentrification then its neighbour, Clapham, is the finished product (Clapham North and Clapham Common, Northern line on the Tube). You could eat/drink/party in a different trio of restaurant/pub/club every night for a week if you had the stamina. In conjunction with Brixton it provides south London with a serious wedge of partying infrastructure - from raves under disused railway arches to the salubrious inner core of the newly-opened Bierodrome on Clapham High Street - if it sounds like the conversation's twice as loud it's because everyone's got a mobile phone and they're all talking at once.

While Portobello Road (Notting Hill Gate Tube, Central, Circle and District line) may be situated in the inner-city it doesn't have the 'grit' of its urban siblings. It is an area that has been well and truly discovered and it lacks the substance of the 'what-you-see-is-what-you-get' redolent of its rougher brothers and sisters. But it does accommodate Portobello Road market which is arguably the most famous avant-garde market (that's posh-speak for second-hand) in London and respect is due. With enough used clothes stalls to stock any aspirant 'shabby-chic' wardrobe and the fatty wafts of the burger van thankfully substituted by the milder aromas of cappuccino and Thai curry it is a pleasant slice of the London pie.

This part of west London hosts the biggest street event in Europe, Notting Hill Carnival (on the last Sunday and Monday of August) which pulls in more than a million people a year. Revellers pack the quaint streets and squares - lined by million pound mansions - to celebrate the country's Afro-Caribbean community. Ground ice drinks, barbequed corn and solid basslines combine to make a heady brew. With the area's high-rise housing blocks nearby providing suitable accomodation for illegal broadcasting operators the area is full of pirate radio stations. On the day of Princess Diana's death 15 home-grown stations blasted everything from drum n' bass to traditional Greek grooves dedicating the music to the "People's Princess" - it was a moment in London's underground history.

There's a popular expression in a very Irish part of London: "Give us back the six counties and we'll give you back Kilburn". Kilburn High Road (Kilburn Park, Bakerloo Tube line) is testimony to the people who built this area and the pub names speak volumes: The Shamrock, O'Leary's. On a good night it's a trip to another part of the globe, on a bad night it can all be a bit heavy - men with glasses collecting for "the boyos". Without confirming cliches the Guinness here is the best you'll find outside Dublin - there's good 'craic' in County Kilburn.

What Camden Lock (Camden Town, Northern line) lacks in tradition it makes up for in size and choice - twenty shades of gothic black; every variety of velvet; joss-sticks with every scent known to science; more African drums than downtown Soweto; record stalls for all. Camden Lock is vastly over-subscribed and the crowds which fill its narrow walkways are often there to look and look alone - for all the people actually willing to buy a hand-knitted Peruvian sweater there's ten who want to watch. Still, the market and the night life the area supports, is world famous and gives swanky Camden a reason to exist.

And from this patchwork quilt of extremities the whole of London emerges. Wealth sits indifferently with poverty; new stands tall over old; tradition pokes its thumb at trend.

While to some our city may taste like a ill-mixed cocktail, to many it is what makes this ancient city so special. The ingredients in this communal cup are always changing - movement and variety is the air we breathe. Blue-haired punks share seats with pin-striped businessmen; Muslim family-run shops sell copies of the Jewish Chronicle. In many ways, anything goes.