As many as 450 of the defective notes were distributed to banks across the country last week, according to the Bank of England.

It said that the affected notes have one of two obvious problems: the raised print on the front of the note is either of very poor quality, or it is completely absent.

In a statement, the Bank said that an initial investigation at De La Rue indicated that sheets of partly printed defective notes, which were meant to be destroyed, had been mixed up with good quality notes and packed for distribution.

It added that the faulty notes could be exchanged for good ones either with the Bank of England or at the bank that distributed them.

The current 20 note features composer Edward Elgar and was introduced in 1999, replacing electricity pioneer Michael Faraday, who had graced the note since 1991. His image had in turn replaced William Shakespeare.