British Olympic hopeful: Muddy, scared – and happy

A Slice of Britain: Careering down steep drops in the rain, at speed, is all in a day's work

Rain and drizzle have set in, turning the hill in front of us into a vertiginous mud slide. This is the kind of Saturday that would persuade most people to climb back under the duvet, but mountain biker Annie Last never has that luxury.

The 21-year-old is Britain's greatest hope for a mountain biking medal in this year's Olympic Games. And this drizzly hill is Lee Quarry outside Manchester, where she comes most days to train. Today she is about to take 12 women and girls for a masterclass around its eight kilometres (five miles) of twisting, steep and rocky track, as part of a push to get more women into the sport.

Last, the UK champion, already has two top 10 World Cup finishes and was twice a world silver medallist at under 23. In a sport where careers often peak in an athlete's thirties, Last has come up quickly and is looking in good shape for a place on the podium.

As she leads the way up the hill, I attempt to keep pace. My usual cycling experience of 15 minutes into work, and even then only when the sun is shining, becomes evident quickly. After about five minutes and a near topple, I take the wimp's route and push up the remaining stretch. Many others follow suit, muttering, "Sod this!" But the real challenge comes at the top.

This is arguably the toughest of all the two-wheeled disciplines, combining the dare-devil jumps and stunts of BMX with long-distance endurance racing. Contests usually take more than an hour and a half, with multiple laps around rugged tracks usually 5-7km long.

Britain hasn't had a female mountain biker qualify for the Olympics since Caroline Alexander at Sydney in 2000. It became an Olympic sport only in 1996, and Phil Dixon, coach for the GB team, is revelling in the country's first serious medal hope. "It's really exciting," he said. "Annie is a developing athlete who is already competing with the best in the world."

Last grew up with outdoor pursuits, in Bakewell, Derbyshire, where her dad ran an outdoor activities centre. Flying through school with four As at A-level, she has deferred a place at Sheffield Medical School.

"It was always my brother that was into cycling. One day he said he said he'd ride a horse if I did a bike race, so I did one and realised I loved it." She admits that Olympic glory was soon on her mind. "I wanted to be the best that I could be... riding for GB and maybe being world champion."

We are taken through some surprisingly challenging braking drills before being taken to the pump track, a series of steep bumps in a circuit with high banked sides. Before leaving for the day I had peeked at a map of the course. Instead of a key, there was a description of how to get to the nearest A&E. Now comes the first indication of why this might be.

Among the fastest round the track is 12-year-old Eve Lyon from Leicester. She has been competing off-road for two years and was desperate to ride with Last. "I'd like to do this when I'm older," she says. "It's exciting to see a girl make it."

Next up is another steep climb. This time I'm determined to do it without walking. Pedalling hard, as soon as I hit the slope, my front wheel skids into the air and I fly backwards into an ignominious muddy heap.

For the final ride, Last offers to take people down a red run (the second highest difficulty grading). Everyone follows, not wanting to appear chicken, but the decision soon seems a bit rash. The narrow pass is largely made up of rain-slicked slabs that drop off at different heights, with a fall in the wrong direction taking you down the sheer hill-face.

As the final stragglers pull through the gate covered in mud, it looks as if Last has won over even the most sceptical riders. Emma Moss, 37, a council worker from Bury, had never done off-road biking until today, and her hands are still shaking. "In traffic I'm fine, but a few rocks and I'm terrified. But Annie was so encouraging."

Though tough, the quarry is a good place to practise for the Olympics: the Games course at Hadleigh Farm in Essex is already being tipped as one of the most gruelling ever. Behind Last, a video shows her flying round the Olympic course. As she soars over a pile of rocks, one of the coaches tells the girls: "There are probably only three women in the world who could go this fast." No place is guaranteed on the podium, but one thing is for sure: Annie won't be last.