AS it drains into a bag, blood is a rich, angry colour. It'd be wrong to say it was red because it is far more of a bruised purple, rather like a ripe plum that's been squashed on the road and is attracting all the flies and wasps from miles around to suck out its juices.

Or so I thought, lying there on my back with a needle in my arm, twiddling my fingers.

There was plenty of time to think as the blood drained out of my arm into a bag. Some people stared at the ceiling; others had brought a small book which they propped one-handedly on their chest. Because I had never been blooded before, I'd brought a big broadsheet newspaper which I flapped pathetically in the air trying to turn the page until a kindly nurse lent a hand.

Everyone twiddled their fingers.

So, instead of struggling single-handedly with the flapping paper, I stared at the chap lying on the next trolley. A youngish fellow, powerfully built in a t-shirt with a pretty wife who came over after she'd finished. In fact, looking around the church hall, most people were more young than old, and, amid their earrings and tatoos, mine was the only tie. Odd, really, as I thought it'd be more older and middle class than it was.

The youngish chap's bag was slowly filling as he idly twiddled his fingers - twiddling helps the blood flow. According to the literature outside, his litre bag contained five billion of his red blood cells. That's 5,000,000,000,000 in a bag no bigger than a shop assistant would put a newly-purchased CD in.

Inside you there are 25 billion, one per cent of which (a mere 25 million) die every day. In fact, in the time it takes to read this sentence 300,000 of your blood cells will have died.

I remembered the most interesting thing in the literature outside: there are more people with blood group O in the North of England than anywhere else. This is because this region's gene pool was largely unpolluted when the Vikings came raping in the 8th century, bringing their group A with them.

The nurse slid the needle from the youngish man's arm and he slowly got up to go for a cup of tea and a biscuit. He was one of the 1.9 million people who give blood annually - just six per cent of the population.

Why? I was there because there I had run out of reasons not to be there. It didn't hurt. It wasn't inconvenient. It wasn't difficult. There was absolutely no reason why I shouldn't be there.

My needle was painlessly withdrawn and my bag was taken away. At the biscuit table, the youngish man shrugged his shoulders. Why? It was just something he and the wife had been doing for five years.

The others around the table similarly shrugged. One woman said she deposited in the blood bank in case her children ever needed a withdrawal; another said it was a family thing as she'd first come down with her dad 22 years ago. Now her daughter was out there on a trolley donating - "she'll take a while 'cos she's a slow bleeder."

There was, though, a warm glow around the table. My first giving of blood, on Tuesday, was a quasi-religious experience. People had been mysteriously drawn to the church hall, had stretched out in silence twiddling their fingers, and had received no other reward beyond a Bourbon biscuit and a pleasant feeling in the soul that they'd helped someone they would never know.

l National Blood Service Helpline 0845 7711 711