The days of spending paper banknotes in the shops are numbered: 100 days, to be exact - so start hunting at home.
The Bank said that around 314 million paper £20 banknotes and 163 million paper £50 banknotes were still in use.
The Bank said the newer, polymer notes were also harder to counterfeit.
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Paper £20 and £50 notes issued by Clydesdale Bank, Royal Bank of Scotland and Bank of Scotland