£1bn worth of £5 notes are lying in the vaults of the Bank of England, but high street banks don't want them.
(Seemingly circulation of the £5 note has not increased in 15 years, but over the same period the average time they remain in the banking system has doubled. This means that those in circulation are really grubby and often torn or damaged. Of course if they want someone to distribute nice, new, crispy ones then I'll willingly help out.)