MY legendary meanness backfired after I insisted on getting 20p back from a shop.

I was at the till at Boots in the Octagon, High Wycombe, when a cashier gave me a handful of change after putting my purchase into a bag.

I walked a few steps away and found I had 20p too little in change. My indignation was pricked and demanded that, on principle, I should get the money back.

However, there was now another customer at the till so I had to butt in to announce I'd been shortchanged. The cashier was good enough to oblige by handing me 20p.

It was one of those slightly embarrassing scenes that makes me cringe normally when someone else does it, and I was the culprit now. But I was in the right, I told myself.

That was until I walked on a few more steps and saw something small and silver tumble out of my carrier bag on to the floor.

It was the missing 20p which had somehow fallen into the bag while the transaction was made. To my horror, I realised it was me who was in the wrong and the cashier had given me the correct change.

One of the side effects of petty meanness is excruciating honesty.

How could I, if my principles were as high as I reckoned, walk away with the four shillings when I'd made such a fuss in the first place?

How could I ever insist on a refund anywhere again if I didn't apply the same standards of probity to myself?

It would also mean, in my limited knowledge of retail work, that the till would be out at the end of the day when the cash was counted. And that would hardly be fair on the staff and the shop.

I vowed to give the money back.

But by now, a large queue had formed at the particular till and the cashier had now changed over. There was no one immediately around to ask, and besides, it would sound a bit potty, wouldn't it, saying to a bewildered shop assistant that I demanded to give Boots 20p back that was rightfully theirs.

Mrs Editor's Chair was in a hurry, so we left the shop. But I mulled on it all afternoon in the Octagon, and returned just before closing time. I honestly couldn't face queuing up to just hand back 20p, because I reckon they would have committed me.

So I looked for something else to buy. The only thing around was an item I vaguely wanted for £10. I took it and strode up to the correct till where there was only one customer now.

But just as I got there, an assistant from another counter called out: "Can we help you over here, sir?" I shook my head and ignored these pleas, looking quite insane as I queued up instead of going to a free till.

Again I ignored the calls from the other counter, and finally it was my turn to be served on the right till. I paid for my new item and then explained that I'd been undercharged 20p from my last purchase.

The girl looked a bit shocked, thanked me and took my coin and I wheeled away in triumph at my virtue.

Only afterwards did it dawn on me, my insistence on getting 20p back had cost me £10.