A dealer has sparked controversy by privately overprinting Post & Go stamps with a stamp show inscription, in much the same style as Royal Mail’s official machine-printed inscriptions.

Rushstamps purchased 6,000 Post & Go 2nd class stamps at Stampex in February, then added the legend ‘Salisbury Stamp Show 2013’ using a 100-year-old letterpress before using them on its mailings in March.

One of Royal Mail’s Post & Go machine operators was unamused: ‘I think the commercial organisation responsible has overstepped the mark somewhat, and that should be stopped so as to not degrade the hobby. If anyone thinks they can just add their own overprints then that really does open the floodgates.’

Royal Mail’s corporate response was: ‘We will be reviewing processes to prevent this from happening again.’

Allan Grant of Rushstamps said: ‘We just wanted to use the stamps as a promotional issue for the show, and to give our custumers something different.’ He confirmed that the Post Office didn’t know about the plan beforehand, and said that all the overprinted stamps were used up on the mailing, and no mint examples exist.

Post & Go collector John McCallum said: ‘I hope no other company will repeat this. I also hope that Rushstamps covered the postage by using stamps that weren’t overprinted, otherwise Revenue Protection could be knocking on their door seeking redress.’

The use of private overprints and perforated initials was accepted in the mid-Victorian period, in Great Britain and in parts of the British Empire, primarily to allow companies to assert ownership over their supplies of stamps to prevent theft by their own staff.

Today, however, unauthorised overprints could be expected to be treated as cancellations, effectively invalidating postage stamps.