'We know that it is a serious matter,' says Mr Leung, a senior environmental protection officer. 'That is why we enforce the law.' Licensing data indicates the SAR has perhaps 13,000 restaurants, and this represents a lot of people who have a restaurant next door or underneath their flat blowing cooking exhausts in and up.

In older districts, 40 to 50 per cent of air pollution complaints may be due to cooking odours, Mr Leung says.

The first step for the department's 'smell police' is to visit a complainant's flat. But unlike complaints about, for example, noise, there is no equipment to measure smells. 'We use our nose to assess it,' Mr Leung says.

If necessary, they can make night visits to see if the smell gets worse when the restaurant reaches its busy time.

Under the Air Pollution Control Ordinance, the Government has powers against any smell that is 'obnoxious' and is either 'an objectionable odour' or which the visiting EPD staff nose considers 'unreasonable for a member of the public to suffer'.

'If we find the odour is causing a nuisance we will go to the restaurant and tell them to take measures to abate it,' says Mr Leung.

If necessary, they can serve an order forcing them to stop producing the offending smell.

One staff member who visits restaurants to serve the notices reports: 'Some of them accept it. But others just can't understand what the problem is.' No one type of restaurant is to blame for most of the complaints: most are triggered by different types of Chinese restaurants which have simply got their vents too close to others' windows.

Generally, it is believed that any place within 30 metres of a cooking vent could be badly affected, depending on the strength of the fumes and the direction of the wind.

However, the days of restaurant smells are numbered. For a start, the department is drafting guidelines on the design and placing of vents to stop cooking smells causing a nuisance.

In addition, the Fire Services Department is demanding that restaurants install hi-tech equipment in which the air extracted from the kitchen is run through a fine mist of running water which is then filtered and recycled.

Although this is aimed at preventing flakes of burning food from causing fires, the Federation of Hong Kong Restaurant Owners' Mr Mark says it also scrubs smells out of the air.

'For the big restaurants, cooking smells shouldn't be a problem,' Mr Mark says. 'But you can't expect a noodle shop to have this sort of water filtration system.' He reckons restaurant owners are increasingly concerned with cooking smells.

'Kentucky Fried Chicken, I think, used to have open frying pans that would have the strong smells coming out over the customers. Nowadays they use closed pans.' Some of these measures can be expensive. The McDonald's outlet in Lan Kwai Fong has its kitchen on the ground floor but takes its cooking fumes up to the roof more than 20 floors above.

'I have heard of complaints, particularly on spicy cooking,' says Richard Feldman, chairman of the Lan Kwai Fong Association, who admits to enjoying a whiff of spice in a restaurant.

But he says that in his area, residents and smells have co-existed without serious problems.

Ironically, the legendary smellmasters who sell 'stinky tofu', or chau dau foo, have little to fear. No-one has suggested putting a hi-tech water filtration system on a hawker's barrow.