Christmas cards are usually a chance to spread a little festive cheer among your nearest and dearest, but this year there’s a catch.

Put the wrong value stamp on your cards - mistakenly or otherwise – and the recipient will find themselves being charged the underpayment plus a £1 administration fee for each card.

Under a new pricing regime being enforced for the first time, larger and thicker letters are more expensive to post. The previous charging system was based on weight.

Postwatch, the postal watchdog, yesterday urged Royal Mail to show the “spirit of Christmas” and waive the surcharges if card senders were unaware of the changes to the charging system. It added, however, that people should brace themselves for the shock of having to pay for the excess postage on a Christmas card that they have been sent by forgetful, or mischievous, acquaintances.

The Royal Mail introduced the “pricing in proportion” rules in August 2006 but waived the underpayment fees last festive season. It said yesterday that it had no official policy to do the same this season.

Andy Frewin, director of Postwatch, said he hoped that Royal Mail would be lenient, adding: “What we are hoping very much is that Royal Mail will apply the spirit of Christmas rather than the letter of their rules and only ask for the surcharges when it is blatantly understamped.”

He said that customers who received a card with insufficient postage would be given a notice to that effect and would then have to go to their local delivery office, queue for service and pay £1 plus the missing postage before they could collect their cards. A Royal Mail spokesman said that while there was no official policy to ignore the surcharges this year, they would be applied using “common sense”.

He said: “Royal Mail always takes a common-sense approach to the tiny fraction of mail with underpaid postage as surcharging doesn’t cover our handling costs, loses us money and is the last thing we want to do – and any suggestion to the contrary is alarmist scaremongering and is just not true.”

When it introduced the changes last year, Royal Mail said that 80 per cent of post should cost the same amount to send. It said the change reflected the cost of sorting large letters which had to be done manually.

For the recipients of understamped cards who are of a miserly bent themselves there is, of course, an easy solution: don’t collect it.

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