Stephen Lewis is up at the crack of dawn to join one of the squads that keep our city streets clean

'Litter is a disease," says Paul Willey. "We're the cure." He is standing in the middle of Parliament Street, brush in hand. It's 5.30 in the morning, and the streets are deserted except for the pigeons which scatter with a flurry of wings as we approach.

Behind Paul, a strange vehicle is creeping down the pedestrianised centre of the street like some kind of exotic, prehensile insect, feelers extended, eyes glowing. It's the 'Schmidt' - the diesel-powered sweeper van which is one of two that patrol the city centre at dawn every morning to sweep the streets clean of litter, and Nigel Smith is at the wheel.

Paul and Nigel are part of the 13-strong litter patrol that clock on at 6am every morning to make sure the city centre is kept spick and span.

They've invited me to join them for a morning's cleaning, stung by a letter in the Evening Press complaining about York's untidy streets.

Such letters, Paul says, are an 'insult' to all of the lads who get themselves out of bed at the crack of dawn every morning.

"At the end of the day," he says, "it's not us who throws the litter down, it's the public. You can come to work some mornings and it's like a bomb site. Nobody ever sees that when they come in to work at 8am or 9am.

"We're not perfect. We can't get every bit up. But we have a damned good go."

Nigel, sitting in the cab of his Schmidt, can't resist having a word too. "It's our own city," he says. "We like to keep it clean."

I'd never expected to spend a morning sitting in a giant, motorised vacuum cleaner: but that's essentially what the Schmidt is.

It is an absurdly fragile vehicle that dips and rocks as you step into it. The seats bounce as though they're on giant springs. Even the floorboards sway and give beneath your feet.

But it can turn on a sixpence and go anywhere: up and down kerbs, across pavements, squeezing between bollards at a gentle walking pace.

Nigel pilots it as it sweeps up and down Parliament Street while Paul runs on ahead, brushing litter out of difficult corners into the path of the Schmidt, stepping on cola cans to flatten them so they're more easily picked up, collecting bottles by hand and dumping them in the litter bins that line the streets.

In one shop doorway on Parliament Street two threadbare blankets are lying forlornly. Probably left by a 'down-and-out' who was moved on by the police, says Nigel. Paul stoops to pick them up and deposits them in a litter bin.

The Schmidt's circular brushes reach and probe like the mouthparts of an insect in response to Nigel's commands, swallowing all the litter in its path. For all its bizarre appearance, the vehicle manages to sound just like my vacuum cleaner at home: and there is the same wash of dry, hot, dusty air in the cab that I get when I've left changing the bag on my own cleaner for too long. But it does a great job.

By the time we've done Parliament Street and have moved on to Pavement and then Colliergate, it's gone 6.30am. A few milkfloats are about, passing with an electric hum and rattle, and a solitary window-cleaner is sponging down a shop-front window. There are a couple of cars around too.

"It's nice to see the world wake up," says Nigel, "and the fresh air is lovely." I stick my head out of the window and take a deep gulp. It's cool and clean, with none of the jaded heat and dirtiness that will fill it once the streets become choked with traffic. There's a certain peace and poetry to the streets at this time of the morning, giant vacuum cleaner or no.

It's not always so pleasant, though. Paul has to walk miles in the course of his work each morning, marching in front of the Schmidt up and down streets and back alleys throughout the city centre from High Petergate to Walmgate. Fine on a nice spring morning like this: but no so great when it's pouring with rain or icy cold.

And weather isn't the only thing Paul and his team have to contend with. Strange and sinister things sometimes happen on the streets of York at the crack of dawn.

The street cleaners often act as eyes and ears for the police, being the first to alert them to signs of break-ins such as smashed shop-fronts and warning of areas where used needles or 'sharps' are dumped. Cleaners are specially trained to collect them.

Occasionally they witness criminals in action. Paul remembers seeing one man jump out of a car, seize a pair of boots belonging to a homeless man sleeping rough in blankets in a doorway in St Saviourgate - and then set fire to him, before speeding away again. It all happened so fast they weren't able to do anything. "Luckily he was able to roll over and put the flames out," says Paul "It was unbelievable."

On another occasion a man pulled up in a van and got out to buy a newspaper from an early-opening shop.

While he was in the shop, someone jumped into the van and drove off. Occasionally, it's the cleaners themselves who are victims.

At 5.30 one morning a few years ago, Nigel was stopped by a man who demanded money. "I said I hadn't got any money, and he slashed my face," he says, showing me the scar still visible at the corner of his mouth.

Fortunately today there's no such drama: simply a city gradually waking up to the day after England's 3-2 defeat by Portugal. Paul and Nigel - whose litter team is just one small part of a city council street-cleaning department which patrols streets throughout the city from 6am to 8pm - had expected garbage left behind by disappointed soccer fans drowning their sorrows the night before.

Actually, they weren't too bad. Probably the fans were too depressed to make a mess, Paul grins ruefully.

One thing's for sure I'll never again take the state of the streets of York for granted.