The medical involves another questionnaire, some basic checks (blood pressure, weight, height, some family health questions; do I smoke?; do I drink?); a chest X-ray and an ECG – all designed to prove I am fit enough to undergo the operation which will be conducted under general anaesthetic.

Fortunately, I'm pretty healthy and from healthy stock. I pass.

I'm then handed consent forms – they need consent to extract the bone marrow; and to use it without fee for the transplant and for research. But first I'm warned that if I sign, I'm obliged to go ahead.

I read the Trust paperwork: "It is essential that you satisfy yourself that you definitely do wish to proceed with the harvest before the patient begins his or her pre-transplant conditioning treatment. This treatment begins 10-14 days before the harvest and on completion of the conditioning the patient is dependent upon the infusion of donor blood stem cells to engraft and start producing the necessary blood cells to carry oxygen and fight infection. Without this source of new cells the patient may quickly die... you are, therefore asked to consider signing of the consent form as a morally binding and irrevocable decision."

I suddenly feel much closer to "my patient" and without hesitation I sign.

A day or two later I am called again by the Trust. They need me to give more blood; they want to do more tests. Can I go to my GP again? This time they arrange courier collection. And then comes the easy bit, the bone marrow donation. I report to the London Clinic one Monday afternoon. I am assigned a private room with my own bathroom, and sit down to watch the first Test against India.

A nurse tells me she has to take a swab from my nose to check for MRSA, then proudly tells me she's worked here for 10 years and never had a case.

I am served a cracking three-course meal, with the option of wine. I've stayed in far worse hotels. I settle into bed early, and am told not to eat or drink after midnight.

Early next morning I am given the go-ahead to take a shower, and then asked to change into a groovy blue spotty smock and dressing gown, put on a pair of anti-deep vein thrombosis stockings and some blue slippers.

It's about 7.30am when we walk to the operating theatre. I'm asked to hop on to the bed and a needle is inserted into the backs of both my hands – "just a small scratch" – and I am asked to lay back and relax. I'm waiting for the "count to 10", but it doesn't come.

The next thing I know I can hear nurses calling my name, and I wake up. It's all over.

A litre of bone marrow has been extracted from my hip/pelvic bone; Prof Morgan is pleased with the way the operation has gone – no problems.

I have four small puncture wounds at either side of the base of my back. I prod the area, it feels a bit tender but it's nothing to worry about.

I am taken back to my room attached to a saline drip; my blood pressure and temperature are checked throughout the day. I am offered painkillers, but decline because I don't have any pain. My throat feels a little sore and my mouth is dry. I drink lots of water and particularly enjoy the blackcurrant sorbet I am served for dessert at lunchtime along with soup, roast pork and all the trimmings.

I feel a little tired but proud of myself.

The next morning my dressings are changed and I'm visited by Lee, a donor welfare officer from the Trust, who explains the protocols of confidentiality surrounding the patient. I can write an anonymous letter and she can reply if she wants.

I am told I'll be kept informed of her condition and if she survives, but if the transplant is successful it will be at least two years before I learn anything more about her – and that's only if she agrees. On the other hand, if the transplant is unsuccessful and "my patient" dies, I will be told. I say I want to pass a message to her; to wish her well.

I'm ordered to take things easy, take a week or two off work, and told to expect to feel extremely tired while my body recovers. And then I'm discharged and I catch the train home.

Forget all those stories you may have heard about donating bone marrow being incredibly painful. It's no worse than the stiffness you might get after a game of football, or when you've done an afternoon's work in the garden.

And, honestly, if this is all it takes to save a life, I'd do it all again tomorrow.