It is a money-saving trick used by the most miserly of penny-pinchers.
But now mail bosses have warned people that re-using apparently unmarked stamps could leave the recipient facing a fine, due to technology which can spot stamps which have been through the postal system twice.
In the past, stamps which had not been marked with an inky franking mark were often considered fair game to be used again – although the practice was technically illegal.
But now the Royal Mail uses UV franking machines, meaning that stamps which look unused to the naked eye are likely to be flagged up when they are put through the post a second time – and the recipient is then forced to travel to the local sorting office to pay a fine.
A Royal Mail spokeswoman said: “Our sorting machines in our Mail Centres cancel stamps by applying marks and a logo. Other stamped items unable to be put through machines are manually cancelled using a number of methods.
“Royal Mail can also detect whether stamps have been used before to protect its revenue. In cases where this has been detected, there will be an extra postage charge to the customer.
“ We would urge all our customers to ensure that they buy stamps from a Post Office branch, from Royal Mail direct or from a reputable retailer, especially in the run up to Christmas”.
Donald Walker, from Edinburgh, was forced to make a 12-mile round trip to his local Royal Mail office after receiving a card telling him that he had a letter which he needed to collect.
When he arrived there, he was charged £2 to pick up the letter – which he found was a piece of junk mail which had re-used a stamp.
The envelope had a sticker on it which said: “Delayed and surcharged. Due to counterfeit/used stamp”.
He said: “The letter was unsolicited mail from a removals firm advertising their business. It is amazing to think that staff from a commercial company peel off stamps and re-use them just to save a few pennies.
“It’s hardly good business sense. I won’t be using them now, as the inconvenience of picking up a letter I didn’t even want, plus the fine, really annoyed me.”
In 2009, the Royal Mail introduced a “tamper-proof stamp” which has two oblong strips on either side of the Queen’s head. These are left on the envelope when the stamp is peeled away, rendering the stamp useless.