Maurice Shevlin writes: “Having just read your article it was like reading what had happened to my assistant here at Brown Edge Post Office.

“A young chap came in holding cash in his hand. He got a bag of sugar, coffee and biscuits and brought them to the post office counter. He then asked for a Vodafone £20 top-up for his father’s mobile. My assistant processed the voucher, but kept it on her side of the bandit screen. The chap then asked what his father needed to do with the voucher. The assistant went through the procedure, but the chap seemed unsure and said he would just pop out to his dad in the car to make sure this was what he wanted. He never returned.”

The assistant went to cancel the transaction, but it would not cancel so she rang first the Post Office help desk then, on their advice, Vodafone. Their response was the same as Rajesh Ganatra received (C-Store, 7 November): sell it to the next customer wanting a voucher. Maurice did this but, like Rajesh, discovered the voucher had been activated within minutes of sale.

“The voucher never left the clerk’s side of the bandit screen, and the chap had no visible camera so how could the voucher number have been activated? The assistant followed all counter procedures, so I was left to foot the £20 loss.”

Maurice has added a further security measure of his own. “All mobile top-up requests require payments to be passed over before transaction is undertaken.”

Good advice: I’d put a sign up, too.

Then I got an email from BW Pash in Andoversford, Gloucestershire: “Wi-fi could be the answer. A mate sat outside in a car with a laptop, hacked into their wi-fi. When Vodafone sent the numbers, he tapped them into his phone, job done.”