The Bank of England has found itself in a compromising position after it turned out that supposed fake £5 polymer notes were nothing more than badly damaged genuine money.

The new waterproof and stain-resistant polymer £5 notes, which were introduced in September last year, have enhanced security and anti-counterfeit features including micro lettering and the Queen's portrait, and have been dubbed almost indestructible and impossible to copy.

However, last week, Wadebridge Police in Cornwall believed that fake £5 notes were circulating in the area. "Wadebridge Police have been made aware of some fake £5 notes in circulation. These are copies of the polymer type but there are obvious differences," the police force said.

The gold imprint of the Big Ben clock tower, one of the new security features, was said to be missing on the supposed fakes, while the holograms at the top and bottom of the note appeared green instead of clear, and were no longer holographic.

The case was referred to the Bank of England to investigate only for the Bank to reveal that the alleged fakes were not counterfeits but in fact genuine notes that had been badly damaged by "extreme use".

The finding is controversial given that when the new notes were introduced, it was claimed they had an extended lifespan, lasting around five years longer compared with their paper counterparts, and were highly durable, such as withstanding a 90-degree Celsius tumble dry.

A spokeswoman for the Bank said: "Polymer notes are stronger than paper notes and last longer in day-to-day use but they are not indestructible. The Bank of England is aware that a small number of polymer £5 notes have been damaged due to extreme use, for example prolonged washing at high temperatures. "

"In some cases this has resulted in the foil Elizabeth Tower [Big Ben] being removed. These notes are damaged genuine banknotes not counterfeits, and a lot of other security features remain intact such as the Queen's portrait in the window and the micro lettering. The Bank has not seen any counterfeit Churchill £5 notes printed on polymer."

This is not the first time, however, that there have been claims that fake fivers of the new notes were doing the rounds. In February, police in Dorset also issued a warning that fake notes were circulating where the design had been copied onto paper, and the Bank of England has launched a number of investigations following other claims of forgeries.

The Bank has launched a free app for smartphones that can be used to determine whether the £5 note is fake or not.

Meanwhile, many people have attempted to prove the new £5 note is not indestructible and it has been found that details can be removed with a pencil eraser.

The Daily Mail newspaper approached the banknote printer De La Rue for an explanation on the damage seen in the Cornwall case, but the manufacturer declined to comment.

The paper £5 notes are slowly being phased out and will no longer be legal tender from next month.

A new polymer £10 note will be introduced in September this year.