"I'm sorry. This has never happened to me before," I said, dumbfounded, struggling to understand what had just occurred.

"Don't worry," she said, offering a sympathetic smile. "It's okay. Really."

We'd attempted it this way and that, and she even tried something I'd never had done to me before. But it always ended in disappointment. Not even the nurse's uniform could help.

"But I've done it so many times, and never once failed," I pleaded.

"In that case, it's not surprising. It's about time this happened. Because it's not the first time I've seen it," she assured me. "It can happen to anyone, you know. We expect it occasionally."

"I'm just so sorry. I feel like I've let you down."

"Look it doesn't mean you'll never be able to do it again. You say you're feeling fit and healthy. I'm sure you'll be fine next time," she said.

But her kind words didn't stop me feeling shameful, guilty, less of a man.

There was no escaping the truth. I knew she'd have to let me go.

For the first time in more than 10 years' experience, my haemoglobin level wasn't high enough for them to let me give blood. I just missed their cut-off point by two measly points.

And it leaves me feeling emptier than you could possibly imagine.

I guess I'll just have to eat more spinach.