When the beat goes on, and on, and on . . .: Emma Cook spends an ear-splitting evening on patrol with the Noise Team in Westminster as they take on the party-goers from hell

It's midnight on a balmy Sunday evening and a beleaguered-looking couple stand on the doorstep of a white stucco house in a leafy Georgian square. 'This is always going on,' says the husband, visibly worn- out. His wife is bleary-eyed. 'Christmas Day was ruined, but we're moving out soon. Thank God it's only rented.'

Luckily, Arthur and Peter are on hand, environmental health officers working for Westminster Council's 24-hour Noise Team, the busiest in the country. Sixteen officers share the 12-hour night shifts, responding to complaints within the hour, 365 days a year. The couple show us into their kitchen, its floorboards and windows vibrating from the sonorous chords of Beethoven's Fifth.

Loud disco music follows ('When the going gets tough] The tough get going]'). The source, it seems, is a loud dinner party on the terrace below. We peer out of the window in disbelief as the guests, seemingly oblivious to the music loud enough to break the sonic barrier, chatter and laugh. To hear each other speak we have to stand in the hall.

Arthur knocks loudly on the basement door. 'I'm from the council and I'd like to talk about the noise levels. It's unreasonably loud. Can we discuss this?'

As with dog fouling and traffic congestion, noise pollution has become an emotive urban issue. It's not just a matter of petty neighbourly disputes over squawking budgies. Pressure groups such as the Right to Peace and Quiet Campaign estimate that excessive noise - from air-conditioning to barking dogs - leads to three murders and numerous suicides each year. Under current legislation, people feel increasingly helpless. It seems that if you live next to the party animals from hell there is little the police can do about it. 'They're allowed to stop noisy cars with defective exhausts and that's about it,' says Peter.

His team actually has more power than the police to deal with such problems. If asking people to reduce the noise fails, they can serve a statutory notice that turns the request into a legal requirement. Then Peter can wake up the nearest magistrate and obtain a warrant to seize offending equipment. About 40 stereos and speakers are piled up in the Noise Team's storeroom, waiting to be reclaimed or destroyed.

The whole process is not as bureaucratic as it sounds: it can take less than an hour. Peter drives and Arthur, mobile phone in one hand and pager bleeping, wrestles with an A to Z. Both 47, Peter is chatty, Arthur more taciturn, perhaps because he has been working for seven nights in a row. Tonight, he is giving the directions. They try to alternate roles: this time it's Arthur's turn to confront and Peter's to drive.

Arthur seems quite fearless about the occupiers' response. Armed with nothing more threatening than a printed legal warning, aren't they scared of physical attack? 'You'd be a fool not to feel nervous,' he admits.

They tell stories about doors being opened by men wielding knives and hammers. 'I just keep them talking,' says Arthur. 'You have to be assertive but not antagonistic.' Peter says that less than 5 per cent of people they confront are aggressive. 'They say, 'Oh, it's the Noise Team' - they almost expect us.'

It's 1am, and our next stop is a grim block of council flats in Marylebone, central London. Three storeys up, in a small flat, a woman points to her floor in desperation. 'Because of that, I've been up for nights now, and I've got to be at work at 6am.'

The television set in the flat below is transmitting a distorted soundtrack of gunshots and whooping Indians. Arthur and Peter pace around her bedroom, conferring quietly. They agree the noise level is unacceptable. 'I'd be careful. He can get very drunk and aggressive,' she warns them.

Four minutes of knocking provokes a hostile response: 'You're making more sodding noise than I am.' Arthur just knocks harder. Eventually the door opens to a loud western and the smell of alcohol. A middle-aged man with a shock of ginger hair and heavily tattooed arms sways in the doorway. 'Whaddya want?' he slurs. Arthur reasons with him gently until he turns down the volume.

In the same area we visit a distraught woman in a smart mansion block. For the past month she has been subjected to her neighbour's weekend rave parties. From her bedroom window we can hear a DJ chanting to a low, thumping bass.

'That's what can incense people,' says Arthur. 'Removed from the music, the higher frequencies get lost and all you can hear is the rhythm - it sounds like malfunctioning machinery.'

After four hours of witnessing complainants and offenders, it seems that anyone - regardless of age, class or postcode - can be the victim of excessive noise. According to Arthur and Peter, those most likely to disrupt the peace are 'white middle-class residents who don't think they're doing anything wrong. It's rarely raves in squats. It's normal people.'

And 'normal people' are making more noise than ever. When the team was set up in September 1992 it dealt with 10,000 complaints in the first 12 months; this year it is predicting about 13,000.

Hot and clammy weather doesn't help either. But now again there are little surprises. One night recently they were called out to a party on a notorious north London estate. 'A woman came to the door. She turned the music down immediately, apologised profusely then kissed us both on each cheek.'