Each year, £2million changes hands as organised gangs break the law to sell what health experts say are unhealthy and unhygienic snacks. In the 1990s turf wars, played out in front of tourists, between machete wielding Albanian hot dog sellers focused the council's attention, which wants them out. But the 'hot doggers' just keep coming.

It's nearly 11pm on Saturday and the smell of frying onions lures the first booze soaked customers of the night to Harry's hot dog trolley.

If business is good tonight Harry, a bald, heavily built Turkish Kurd will sell around 60 to 70 hot dogs from his position on Charing Cross Road.

Each sausage - although it is up for debate whether the combination of rusk, fat and mechanically recovered pork and chicken on sale qualify as sausages - costs him just seven pence but are sold for s3 a pop.

By the time Harry packs up at 5am he could take about s200, but most of the money won't go into his pocket. On a good night hot dog traders bank around s70, cash-in-hand, with the rest going to the gang boss who provides the trollies, transport and food.

It is still a decent wage for people whose dubious immigration status means they can not work legally, but Harry is not happy.

His spot, opposite the Cambridge theatre, is in Camden. Tantalisingly close on the other side of the Charing Cross Road is Westminster, home to most of the late night bars spilling drunk and hungry people onto the streets.

"I could sell 100 hot dogs tonight if he would let work just across the road," he says pointing to Gordon Corbett, of Westminster Council's street licensing enforcement team, who is hovvering nearby.

Corbett and his team are every hot doggers' nightmare. They scour the streets into the small hours playing a nightly cat-and-mouse game with the traders, who trundle off into the distance at the sight of them, only to return half an hour later to flog their hot dogs.

Over the months the team has established a strange relationship with the gangs, they are all on first name terms but still have to walk a tightrope between being too harsh, and risking a violent confrontation, and clamping down on the illegal trade.

The aim tonight is to catch Harry - not his real name - and his fellow hot doggers, if they raid across the borough border into Westminster.

Working with the police Corbett has the power to seize trollies and gather evidence to prosecute repeat offenders.

They have at their disposal a Met police van, with CCTV, and can call on police officers if they are going to seize trollies.

And they are pretty good at it too, judging by the 100s of seized trollies in storage in a council lock-up awaiting destruction. Each one is custom made for between s50 and s200, and taking them off the streets puts a dent in the hot dog gangs' finances.

But the big money to be made in hot dogs means the traders head straight back onto the street, often on the same night thwarting Corbett's efforts with the trollies kept in reserve in a van parked nearby.

Tonight over 30 of them from five different gangs are working.

"The scale of the business is staggering, they operate every night, but obviously Thursday to Saturday are the big ones for them, and us," explains Corbett, who has been with the team for five years.

"They are also well organised and have spotters who tail us all night. They phone ahead and let their friends know where we are so by the time we get there they've packed up and gone around the corner."

With fast food chains closing relatively early across the West End, selling hot dogs to hungry boozers stuck in central London is a niche market and one the gangs are determined to preserve, with violence if necessary.

"The more sucessful we are, the more desperate they become. Officers havebeen attacked, threatened and even had boiling fat thrown at them while they tried to seize a trolley. We're trying to put them out of business but they keep coming back because the demand is simply huge," he adds.

The danger is ever-present Corbett and his team, who do not want to be identified in case they are singled out for retribution by the gangs.

"In this job you make a lot of enemies," one adds. "People get nasty when you threaten their livelihood. But to be honest the general public are at least as unpredictable, especially after 10 pints."

The team tackle a raft of illegal trades in the West End including fake DVDs, toys, cigarettes, unlicensed ice cream vans and cramelised peanut sellers. But hot dogs are the main priority.

Harry has just paid the last installment of a s2,000 fine for illegal trading. That he is back on patch risking another hefty fine indicates just how lucrative the trade is.

At night rival firms of hot doggers vye for custom around Regent Street, Piccadiily Circus and Covent Garden, while Westminster Bridge and the London Eye are top daytime huants.

"There're plenty of customers, the people don't care what's inside the hot dogs, they are hungry and we give them food. There is nothing wrong with what we sell," he says, although he hesitates tellingly before saying he eats hot dogs himself.

Harry is part of the Charing Cross Gang, as the council enforcers call them. They are Turkish and Iraqi Kurds from north London and are all related to eachother. Most don't have work permits and are part of the endless stream of traders forced to take up cash-in-hand jobs.

The ethnic profile of the traders changes with the times. It used to be that opportunistic Londoners would operate a pitch until they were moved on, but they were nowhere near as numourous, well organised, or viscious as the Albanian gangs which took over the trade in the early 90s.

They sent out over 60 hot dog trolleys each night and with it a frightening level of violence and several stabbings were reported as rival gangs fought turf wars with foot-long steak knives and machetes in front of shocked tourists.

A joint Westminster Council and police crackdown put them out of business, only for the Turkish Kurds to emerge as the dominant force.

More recently Polish immigrants struggling for work have been picked up.

Most do not know what they are doing is illegal and few have ever heard of health and safety laws.

"That's why it's hard to villify them," says Gordon. "The guys on the street are just foot soldiers. Most of them are ok, just making a living from the opportunities open to them. The bosses rarely come down here, but are making a fortune out of the illegal work of these people."

Every night trucks ghost into the quiet side streets around Holborn to drop off the traders and their trolleys. There, on the southern fringes of Camden and free from the jurisdiction of Westminster Council patrols, they heat up the hot plates before pushing the trolleys towards the borough boundary.

Westminster Council are determined to stop the trade and use a raft of licensing, health and safety and trading standards laws to keep the pressure on. The City Hall view is that it is an unlicensed, unhealthy and unhygienic business which encourages hoardes of drunken people to prolong their evevning in the West End and poses a potentially serious danger to the public - each hastily assembled trolley carries 13kg of gas to heat the cooking plate.

But short of mass, repeated raids to clear the hot doggers out for good, the council is targeting the demand side of the trade. It recently published a study showing a typical street hot dog contains about 37grams of fat, 650 calories and three grams of salt. Then there's the food hygiene issue.

At council-owned warehouse, rows of confiscated trollies still reek of oil and burnt onions. They have all been cleaned by the council, some several times, but oil stains and congealed fat remain.

Most sellers lack even a basic knowledge of food safety, cleaning their hot plates infrequently and even storing cooked sausages left over from the night before in the same box as the uncooked ones. It is the perfect combination for food poisoning, Corbett says.

"There isn't any capacity for refrigeration or hand washing. But they know full well that their customers are transient and even if they get ill they won't be coming back to complain. Besides most people who wake up with a dodgy stomach will balme the 10 pints they had the night before rather than the hot dog."

There is also a sinsister underbelly to the business.

Both the police and council suspect that money made on the street is used in another criminal enterprises.

Direct links have not yet been established but the tightly-knit ethnic communites involved in the hot dog trade are the same ones known to operate other illegal businesses, like people trafficking, drug dealing and prosititution in parts of the capital.

So why not license them, take taxes and legitmise the trade?

"It's not a good idea," explains Corbett. "There's so much cash to be earned that there'll be a turf war between the illegal sellers and the legitimate hot dog sellers who get the licenses." The council is also loathe to encourage late night businesses which attract rowdy and drunken crowds.

Back on the street Harry says he is feeling the pressure but will not be forced out of selling hot dogs.

"I don't have a work permit and must work for my family and children. The council keeps taking our trollies and they make it very hard. But I'll come back, they can't always follow me."