'They arrested the gorilla!'

On the concourse at Liverpool Street station, two men dressed as Tower Bridge are dancing a slow waltz. Their partners are a gorilla and a sex doll that has Boris's beaming face. This is not a strange dream: it is the last party of Ken Livingstone's London.

When I first signed up on Facebook for a final boozy toast to Ken on the Tube, I imagined a few hundred people would appear - but I underestimated my city. As I enter the station, the crowds begin: goths and bankers, Asian teenagers and posh white women, all waving their bottles of Guinness and Blue Nun.

The plan is that we will all clamber on to the first three Circle line trains to leave the station after 9.02pm. As I push through, I bump into a man who is on his knees, a tube in his mouth, with his friend pouring lager directly into his gullet. A chicken carrying a banner which says "People Not Profit" tells me: "Boris symbolises everything we hate. He's not our London." Every time a train pulls in, the crowd whoops and yells "Ken! Ken!"

Hundreds heave on to the first party-train, but as it leaves the Tannoy announces: "This is a security alert. Evacuate immediately." I squeeze out next to Nat Hill, an advertising executive encased inside a giant inflatable horse. "I am dressed like this because I think now we have to be allowed to take horses on the Underground," he says. "Horses are better than alcohol, obviously, so if Boris bans alcohol, he has to allow horses, doesn't he?"

More than a thousand people throng in the centre of the station, and I mingle among the booze fumes and costumes. A lean Brixton-boy says: "I think the drink ban is probably a good idea - but let's party!" Then the crowd is suddenly united with one chant: "Boris is a wanker!"

A group of Essex lads dressed as the Village People stand high on the platforms above, leading a stationwide cover-version of YMCA. A conga line forms and, at 10.17pm, a sound system covered with Free Tibet stickers appears. We all begin to dance, and there is a random cry of "Dalai Lama! Dalai Lama!"

At 11.01pm, boys gyrate on top of ticket machines, and a girl rides the information sign like it is a pony. A friend who got on the party train calls. "They arrested the gorilla!" he cries.

At 11.14pm some idiot starts smashing bottles. Other people tell him to stop, and a few guys start trying to clear up the crunchy carpet of cans and bottles so it doesn't look so bad. But it's too late: the police, who have been watching from the platforms above, swoop.

A girl slurs to me: "I am going to stand by the Cornish pasty shop. Nothing bad can happen next to a Cornish pasty shop."

The police form a line and start pushing people out. A few more protesters foolishly throw bottles. Everyone is chanting again. Pushed out onto Bishopsgate, the crowd looks now as if it will dissipate. But then, suddenly, a bongo-player appears from nowhere, and we all begin to dance again, long into the night.