London Zoo: Did we leave anyone in the tiger's den?

One day last week I arrived home with straw in my hair and a vivid bruise on my calf where I'd been pecked by a penguin. But most alarmingly, I smelt of tigers. I'd just spent the day at London Zoo, where five of us had taken part in a dry run for the forthcoming Keeper For a Day scheme. Our guide, mentor and protector was the enthusiastic and energetically Amazonian Jane Harvey, one of London Zoo's senior keepers.

Our first stop was the giraffe enclosure where Dawn and Crackers seemed pleased to see us. Our duties came at either end of the digestive process and involved sweeping the giraffes' enclosure and feeding them breakfast. Only close up do you appreciate quite what extraordinary creatures giraffes are. Their tongues are deep, dark blue, to protect them from sunburn, and their coats are a beautiful yellow and brown patchwork of squares and hexagons. Most peculiar of all, given their size, their droppings are relatively tiny, the size of shrivelled damsons. As we swept, it felt odd to be on public display. Two toddlers careered up to the wall and peered over. "Hello big bum!" one shouted. I exchanged a sympathetic look with Crackers. Brian, the giraffe's keeper, smiled and shook his head. He was born up the road in Kentish Town and has worked at the zoo for 39 years. As one might expect, he recognises shoddy work when he sees it and when we announced that we had finished, he sent us back to do it properly.

The penguins were the next species to benefit from my benevolent incompetence. They were previously resident in Berthold Lubetkin's Grade I-listed pool, a blue and white 1930s Modernist construction celebrated by architects for its two spiralling intertwined ramps. Unfortunately, this innovative use of materials was lost on the penguins, who struggled in Lubetkin's egg-shaped landscape. They much prefer their current home, which more closely resembles a natural habitat. Our job was to scrub green and white poo from the edge of the pool. We were warned to stick together; if a penguin should misbehave, Jane told us, the sort of firm "no!" one might direct at a toddler would do the trick.

Resting on my scrubbing brush in the warm spring sunshine, I wiped my brow. As I caught my breath, a sharp pain shot up my leg. "Excuse me, Flash. No!" Jane called out as I hopped around with a penguin attached.

Over a hearty lunch in the staff canteen, we talked about childhood pets and Jane swapped tips with Katrina Boardman, the Australian keeper who runs Keeper For a Day at Whipsnade. Both projects are run by the Zoological Society of London, founded in 1826 and now a charity, and it could raise up to £75,000 a year via 525 places. This money will fund the zoos at London and Whipsnade as well as scientific conservation and research programmes in 30 countries.

Now that we had relaxed it was time for a shock. Like Clarice Starling on her way to see Dr Hannibal Lecter, a grey-haired Irish keeper called Matt led us into the home of Raika and Lumpur, a pair of tigers. Matt clanged heavy metal doors, checking, double-checking and checking once again that the barrier between man and feline was secure. Even so, a yellow line on the floor advised you not to cross lest you come within range of a swiping paw. As a metal door slammed, Raika and Lumpur strode in. And they didn't look happy to see us. Hearing a tiger roar close up is unnerving. It is a deep, vibrating and profoundly frightening rattle that echoes off the walls. The tigers' smell is a strong and musty scent somewhere between wet straw and ripe meat, while its eyes have a look of violent, almost psychopathic indifference.

Matt talked about the risk of extinction as he ran horse meat with the hair still attached up a pole to feed them. Of the 650 species at London Zoo, 112 are listed as threatened and it participates in breeding programmes for 130 species. In the background was the unfamiliar but unmistakable sound of crunching bone as a 170kg tiger feasted on a slab of horse.

"Have we got everyone?" Matt deadpanned as we stepped out into the fresh air. As if we had thought for a split second about staying behind.

Keeper For a Day is run by the Zoological Society of London and costs £150 for an introductory session or £225 for a full day at London Zoo or at Whipsnade Zoo in Bedfordshire. It is open to over 16s (keeper foraday.co.uk; zsl.org).