There was no reason for doing it other than the number 27. My friend Zorica and I needed to mark that unremarkable birthday. There happen to be 27 stops on the Circle Line. A beat-the-clock Underground-overground pub crawl seemed a logical, grown-up solution.

We half-hoped that somebody might talk us out of it. Besides, who would want to join us to waste 12 hours jumping on and off Tubes, racing into pubs, downing half-pints and pissing off landlords and locals from Paddington to, er, Paddington? Physically fit beer monsters? Ex-pat antipodeans? We'd forgotten that most of our friends fell into one or both categories.

So, I took it upon myself to do a recce of pubs nearest the stations. I even drew a map. Everyone understood the race-against-time concept and knew what a circle looked like, but there was no margin for error. If we were to make it round before last orders, we'd have half an hour per pub. That included travelling and squabbling over whose round it was.

Nobody thought we'd actually do it - and the day didn't start promisingly. Eight of us met at Paddington at 11am: three got lost on the way to the concourse bar; one of them was Zorica. When we reconvened, it was 11.15. Despite enthusiastic promises of success and glory, the first lager was a struggle. I'd only had muesli for breakfast, and I couldn't remember the last time I'd been awake before midday on a Saturday. When we finally hit the Circle Line, somebody asked which stop we were getting off at.

At Edgware Road, 16 New Zealanders followed us into the pub, finishing well before us. At Baker Street, we were met by a few thousand Orient fans. It took us five minutes just to get inside; then Antony, our own Kiwi Circle Line-veteran, started reading the paper. It wasn't looking good.

Then suddenly we were off. By Great Portland Street, we had six more recruits. At King's Cross, we passed more antipodeans who were "doing" the Monopoly Board. (The jail stop must be interesting.) At Barbican, the circling Kiwis had been and gone before us; they'd also used up "the warmest welcome" boasted outside the pub. "The Circle Line isn't a new thing," growled the barman on our exuberant entrance.

We hopped through the City on uncommonly regular trains, peered into six designated, but closed, pubs and took in the sights at Tower Hill. We also notched up three identikit Wetherspoon's pubs in two hours.

At Embankment (stop 18, pub 12, 6pm) we lost four friends, who had better things to do than watch the birthday girls disintegrate, but gained three more, worryingly sober. At Westminster, a storm nearly ended our progress; by St James's Park, pints were appearing and photo-calls descending into anarchy. At Sloane Square, a friend decided a fireman's lift was what I needed. It wasn't.

At this stage, I'd like to apologise to pubs from Gloucester Road to Bayswater. We converged with our Kiwi rivals on the same pubs and slammed tequilas with them when we finished, 30 minutes ahead of time. I'm glad I couldn't see myself. Funnily enough, I can't remember myself either.

Apparently, the journey home involved team gymnastics from the carriage bar rails. I hate people who do that. The other passengers weren't so much amused as terrified. The last my friends saw of me I was cartwheeling across Ealing Common. Except I kept forgetting to put my hands down first.