For those uninitiated in the ways of Waitrose in Worcester Park, when you complete your purchase at the checkout, you are handed a small green plastic token.
The checkout person will then chant the familiar mantra: "Are you familiar with our charity token system, Sir?"
I am, of course, but occasionally I will feign ignorance and watch the fixed smile fade slightly from the face of the assistant as they explain for the thirty-fourth time that day that:
"You place the token in the box of of your chosen charity, then at the end of the month Waitrose will make a donation to the charities on your behalf"
All well and good. Except that today I ran off with one of my green charity token. It was only when I got to my front door and reached into my pocket to retrieve the house keys that I realised the heinous act that I had perpetrated against charity.
Now I know what it must feel like to snatch food from the mouth of starving orphan, drag a gasping whale further up the beach or pee in the only water supply for an African village. Such was the extent of my crime against charity.
Oh the guilt, the guilt. Of course I will be returning it on my next trip to Waitrose, but it got me thinking about the odd sport of 'charity choosing' at Waitrose.
There is something strangely compelling about this monthly beauty pageant of charities. This month the Surrey Air Ambulance is whipping the pants off the Worcester Park Brownies (only metaphorically, thank goodness) and Victim Support Merton aren't doing very well either.
Presumably this is because the middle-class folk of Worcester Park care little about having their shoes shined and wouldn't even dream of going to Merton, let alone being mugged there.
The three charities change every month, and so begins another fascinating window into which causes the middle classes of Worcester Park hold dear.
Now, remind me to return that token next time I go. If the air ambulance runs out of fuel then I wouldn't want that on my conscience.