Richard Curtis: It's shocking how easy it is to save a life

David Walliams during his attempt to swim the entire length of the River Thames to raise money for Sport Relief (PA)

I've been working on Comic Relief and Sport Relief for 27 years now and still feel the same passion for it as I did at the start, when I wandered around Ethiopia in the middle of the famine in 1985 wondering whether I could think of anything I could do to help. I still feel the same daily shock at how easy it can be to change other people's lives – and the same daily horror at how mere geography lets us live contentedly in a world where people starve to death. And the same daily delight at how wonderfully generous people can be with their money and their time and their talents to help.

But also, right from the start, there's been an element of chaos to it all. I remember in 1985, the night I arrived at Wollo in Ethiopia, I was staying in a room with no door, and thought I had better not leave my camera out, because it was so important that I took pictures the next day. So I took the camera into bed with me – and during the night rolled on it, and broke it.

The next day, I saw the most terrible sights of my life and was encouraged by the camp workers there to take pictures, so I had some evidence to show people back home. I didn't have the nerve to say I had broken my camera – so I pretended to take pictures anyway. I spent the day, in front of a thousand malnourished children, pushing a broken button, saying "thank you", and moving on, ashamed.

And since then, for all the wonderful things that have happened with Sport and Comic Relief, there has always been a share of debacles. I offer these up to encourage you if you've got some fabulous fund-raising thing organised, and it doesn't really work out. I know exactly how you feel. Press on – it may still go better than you expect.

The Vegetable Play

Fundraising in schools has always been absolutely key to our success – and, one year, we came up with the cracking idea of writing a little play that every school in the country could perform on Red Nose Day. Fresh off the back of writing Four Weddings and a Funeral, I was pretty sure I was the man for the job.

I wrote a 15-minute epic, in which children had to dress as various vegetables – and there was a very good moral at the end about social justice and parsnips or something. We sent out 22,000 copies of the play to the UK's schools. Final research revealed that, in the end, eight schools performed it. We never found out the total money raised. But it wasn't a lot. In the region of £50. Or a bit less.

The Building Nose

They were huge, they were to be tied to buildings. We were so confident they would raise money, we sold them for £1,000, thinking we'd make a massive profit. We didn't. There were planning issues. There were why-the-hell-would-we-stick-a big-bit-of -ugly-red-plastic-on-to-our-beautiful-building issues. In the end, we just broke even. We didn't do it the following year.

The Running Order Cataclysm

Probably the worst mishap was one Night of TV when the running order timings went wrong. The running order is the holy grail of our show, with careful timings of every link and every piece of pre-recorded material meticulously planned. Somehow, I ended up with a running order that had "zero" attributed to all of the pre-records, so, as I discovered about 20 minutes after the show started, we had five hours of material to squeeze into three hours before the News.

The first pair of presenters, meant to finish at 8pm, finished at 8.45pm. It was a tough moment when I had to tell Zoe Ball and Johnny Vaughn that their carefully rehearsed, hour-long section was now a 15-minute cameo. They eventually bounced off at 9.15pm – and that was where the real trouble started. Presenting the final, pre-News hour were Dawn French and Jennifer Saunders, who tend to expand a bit when they're having fun and like to ignore the autocue.

The crucial thing is that, in the 10 minutes before the News, we show some very emotional appeal film which gives people time and motivation to donate. French and Saunders were beginning a long bit of glorious improvised fooling around when we hit 9.50pm. I knew that every amusing moment was now costing lives. I got a large piece of paper and wrote on it, in big felt-pen, "FAINT!" Dawn saw it out of the corner of her eye – and fainted. Jennifer looked puzzled, looked to the autocue – and saw "And now a film from Kenya". She said it, and we were back on track. And Dawn was still pretending to be dead.

The Goat

During the first year's filming in Africa, Griff Rhys-Jones recorded a passionate appeal in Sudan holding a goat, explaining how the public's money could pay for "goats like this one" which were crucial in the battle to restock herds. In turn, these goats would revive a local economy ravaged by drought. We broadcast the film many times that year, not knowing that after filming, a friendly Sudanese guide had informed him that the animal he had been holding was actually a sheep.

I haven't mentioned Billy Connolly grappling naked with an alcoholic in the foyer of the Piccadilly Theatre, Patrick Kielty getting arrested in India, the spectacularly unpopular touring Millennium Gnome, or the colour-changing car noses that didn't change colour. I apologise for them all – and all the other well-meaning disasters.

But for all the ups and downs, we have fundamentally stayed on track. I'd encourage everyone to watch Sport Relief tonight – it feels like it's going to be one of our best ever shows – and if you've got any cash to spare, please ring it in.

Lives are still in the balance every day, home and abroad, and Comic Relief has got 20 years of experience spending it where it makes the most difference, whether it is paying for a child in Sierra Leone to get a vaccine or a woman in Sunderland to get away from a house of domestic violence.

You can actually save a life. You won't really know what you've done – but sometime next year, somewhere a father will be holding in his arms a child who has recovered from malaria, and it will have been your fingers pushing the Donate button tonight that did it.