Why should I have to wear a face mask to give blood?

Any day now I shall be frogmarched, or at least very firmly escorted, out of a blood donor centre in London. I know this is going to happen because I made the appointment weeks ago and I intend to keep it. But when I signed up to donate my pint of blood to the public good, I was not required to wear a muzzle during my donation. Now I am. I do not intend to do so. I find the idea of donning one of these face-nappies physically repulsive, and dislike the mouthless, submissive appearance they create in all their wearers. I also believe them to be futile. I know the government believes this too, because it was saying so only eight weeks ago, and there has been no great scientific discovery since then.

But above all, I am severely distressed by the obligation. I should not be forced into such a gesture.