Royal Mail is investigating issues with its new barcoded stamps as customers are being wrongly fined for receiving letters, reports suggest.

Members of the public have been complaining to Royal Mail that they are having to pay £5 to collect post which has been deemed to have counterfeit stamps on it.

It is alleged that fake stamps were purchased from Royal Mail directly, leading to fears they are being wrongly labelled as counterfeit.

The Telegraph reports that a formal investigation has not been launched, but that Royal Mail is working with retailers to identify the “source of the problem”.

Post Office minister Kevin Hollinrake told The Telegraph: “We spoke to Royal Mail and they are investigating and they are working alongside the Post Office and other retailers to try and ascertain the source of the problem.”

The postal service switched to an entirely barcoded system in July, with barcoded stamps becoming mandatory on July 31.

However, a number of complaints emerged in the run up to Christmas as cards were either left undelivered or could only be collected if the recipients paid a £5 fine.

The Post Office said the allegations were “extremely serious”, and said it received stamps directly from Royal Mail’s secure printers.

After printing they are delivered to a Post Office warehouse before individual Post Offices receive the stamps via specialist delivery vans.

A Post Office spokesman told the Telegraph: “Any allegation that fake stamps have been purchased at a Post Office are extremely serious.

“The implication of such an allegation is that one of our postmasters, or a member of their staff, has obtained fake stamps and has chosen to sell them to customers rather than selling legitimate stamps that have come from Royal Mail’s secure printers.

“This is why we insist that any customer who thinks they may have purchased a fake stamp from a Post Office must produce an itemised receipt so that this can be looked into further.”

A Royal Mail spokesman added: “When a customer reports to us that they bought a stamp from a retailer that is subsequently found to be counterfeit, we will always look into the circumstances of that case.

“We also work closely with retailers and law enforcement agencies, and actively seek the prosecution of those who produce counterfeit stamps. We reaffirmed that policy to the minister today.”