The foul smell is ominous. Downstairs in a central London pub, a woman has passed out on the floor of the ladies toilets, lying on the cold tiles with her dress pulled above her waist and knickers at her feet.
Intoxicated and at risk of choking on her own vomit, this is no teenage tearaway but a respected economist and middle-aged chief executive of an international company. It is Christmas party season in the City.
At this time of year, it is not only the usual distressing soaks the paramedics need to help sober up, putting them on drips or pumping their stomachs. Bankers, lawyers and accountants – celebrating the end of the working year with jollies that start at lunchtime on empty stomachs and stretch into the night – form one of the biggest demographics requiring medical help for alcohol abuse.
The problem has become so acute that in these last days before Christmas, a field hospital has been set up in the heart of London's financial district to treat blind-drunk revellers and take the pressure off hospitals and the ambulance service.
At Liverpool Street station, a group of paramedics and St John Ambulance volunteers shelter in a tent, huddled over sweating, slumped forms, the casualties of another night battling the sauce. Inebriated financiers are wheeled in, tied to gurneys; dribbling executives lifted are in on stretchers.
One of the early call-outs the unit receives is to a nearby chain pub, where an investment banker has collapsed on the floor after falling off a chair he had been standing on.
Watery-eyed, and with his hairy belly hanging out the bottom of a navy jumper adorned with a thin sliver of vomit, he claims he has had "four or five beers" as he is strapped into the ambulance to be taken to the Liverpool Street field hospital.
"I don't normally do this," he tells the crew.
"We know," one of them replies. "But we couldn't leave you laying in your own vomit."
Although he slumps forward and is barely able to keep hold of the cardboard bowl that he continually spits into, the nattily dressed young man manages to speak reasonably clearly when a member of the crew asks him for his address: "25," he says. Asked for more detail, he replies: "25 October." The paramedic smiles and repeats the question. "25 October," he insists. "I'm not lying." Back at the station, a more sober friend arrives to consider options for getting him home. "I thought you were dead," she tells him with a rueful smile.
This weekend saw the big one, what the paramedics call Black Friday, the busiest evening of all, when many big companies hold their Christmas parties.
The London Ambulance Service has three ambulances and a car for alcohol-related incidents, to allow other vehicles to deal with more serious emergencies in the area."I like a drink as much as the next man," says Nick Lesslar, a duty station officer for the service who devised the field hospital.
"Tomorrow night, if I'm not on duty, I'll be having a drink. I go out to parties, have a lot to drink with my mates and feel really nice. But I've never got myself into the state we see some of these people. I've never been in a fight and I get home in one piece."
When a crews arrives at the scene, the lead clinician decides whether the patient can be dealt with at the Liverpool Street tent hospital or if they need to be taken to accident and emergency.
The team of emergency workers are good-humoured and patient with their drunken charges. According to Mr Lesslar, 80 to 90 per cent of the calls his crews deal with on any Friday or Saturday night during the year are drink-related, and so they are practiced in dealing with the effects of over-consumption.
Nevertheless, he admits to being baffled by many of the patients they take in. "What surprises me is the very well-educated, clever people who have had a slice of toast for breakfast, cocktails at lunchtime and have gone out drinking all night.
"We had one lady last year who worked in a posh office, an investment bank. She was really well-dressed and she had vomited all down herself. It was in her hair, everywhere. They just don't get the concept that you can't drink all that on a piece of toast."
He is interrupted by the arrivals of another banker, dressed in his dark suit and rumpled pink tie, brought in be rehydrated, and a well-spoken young woman in a smart, black, sparkly dress. She is comforted with some water and a blanket before being led safely to the front of the taxi queue.
"We don't let them get comfortable," Mr Lesslar says. "We don't just lie them down on a stretcher and sleep it off, because they will bed in for the night. Better to rehydrate them with tea or coffee."
About one in three was sent to the hospital, including the executive on the pub toilet floor. "Lots of these people just don't plan their journeys home," Mr Lesslar says. "They are mostly very grateful."